Protective film for polarizing plate

ABSTRACT

A protective film for a polarizing plate is disclosed in which an contact angle of the surface in contact with a polarizer with respect to pure water is less than 55° and the surface in contact with a polarizer becomes hydrophilic due to a plasma treatment.

This application is a divisional application of application Ser. No.10/300,400, filed Nov. 20, 2002, now allowed, which is a divisionalapplication of application Ser. No. 09/548,939, filed Apr. 13, 2000 (nowU.S. Pat. No. 6,512,562), which is hereby incorporated in its entiretyherein by this reference.

FIELD OF THE INVENTION

The present invention relates to a protective film for a polarizingplate, which exhibits excellent adhesive properties, and a polarizingplate employing the same, and a production method thereof, and furtherto a production method of cellulose ester film which exhibits excellentrecycling properties.

BACKGROUND OF THE INVENTION

As a protective film employed in the polarizing plate of a liquidcrystal display, cellulose esters such as triacetyl cellulose and thelike, are suitable due to their lower double refraction, and havefrequently been employed.

Commonly, a polarizing plate has such a structure that a polarizing filmcomprised of a polyvinyl alcohol film and the like, in which iodine ordyes are absorbed and oriented, is laminated on both sides withtransparent resin layers. Frequently employed as said transparent resinlayer is a protective film comprised of triacetyl cellulose film.

When a polarizing plate is produced by adhering a protective film with apolarizer, in order to readily apply a water-soluble adhesive, aprotective film such as triacetyl cellulose film, and the like istemporarily subjected to saponifying treatment through immersion in analkali solution having a high concentration at a relatively hightemperature so that the film surface becomes hydrophilic. Then, anadhesive is applied to said protective film which is adhered with thepolarizer. However, it is preferred to make a transparent resin filmhydrophilic without employing chemicals for saponification, which arenot preferred in view of work as well as troublesome processes.

Further, for a transparent resin film employed as the protective filmfor the polarizer, triacetyl cellulose is exclusively employed. One ofthe reasons why triacetyl cellulose has not been replaced by other filmsis that the other films are not subjected to saponification.Accordingly, another process, which replaces saponification, has beensought.

The present inventors have investigated various methods to make thesurface of a transparent resin film hydrophilic, which replacesaponification. As a result, it has been discovered that when atransparent resin film is subjected to plasma treatment, it exhibitssimilar performance obtained by saponification.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a highly efficientprotective film for the polarizing plate, which is readily adhered withpolyvinyl alcohol film employed as a polarizer, can be producedemploying processes which are safe in view of operation and do notadversely affect the environment, and exhibits excellent adhesion with apolyvinyl alcohol film layer, and a polarizing plate employing the same.

Further, another object is to obtain a protective film for thepolarizing plate, in which moisture resistance is enhanced employingsafe methods for operation, and which exhibits excellent durability.Further, it is possible to obtain a protective film for the polarizingplate, which comprises cellulose ester film which is readily recycled.Still further, it is possible to obtain a polarizing plate as well as aliquid crystal display unit which exhibit excellent durability.

An outline of the present invention will now be described.

1. A protective film for a polarizing plate comprising: a base material,the protective film for the polarizing plate wherein in analysis ofbonding state of a carbon atom (C1s) employing X-ray photoelectronspectroscopy, when a peak having the lowest bonding energy is designatedas a first peak, a peak positioned at 1.60±0.3 eV on the higher bondingenergy side from the first peak is designated as a second peak, and apeak positioned at 4.10±0.3 eV on the higher bonding energy side fromthe first peak is designated as a third peak, bonding state of carbonatom C1s on a surface of at least one side of the base material andbonding state of internal carbon atom C1s in an optional depth of 0.05to 1 μm from the surface satisfy relationship described below:S−I≧0.1

wherein S is intensity of the second peak on the base material surfaceof the protective film for the polarizing plate/intensity of the firstpeak on the base material surface of the protective film for thepolarizing plate, and I is intensity of the second peak in the interiorof the base material of the protective film for the polarizingplate/intensity of the first peak of the interior of the base materialof the protective film for the polarizing plate.

2. A protective film for the polarizing plate described in claim 1,wherein S≧1.60.

3. The protective film for the polarizing plate described in claim 1,wherein the bonding state of carbon atom C1s on the surface of theprotective film for the polarizing plate satisfies relationshipdescribed below:T≧0.2

wherein T is intensity of the third peak on the base material surface ofthe protective film for the polarizing plate/the intensity of the secondpeak on the base material surface of the protective film for thepolarizing plate.

4. The protective film for the polarizing plate described in claim 1wherein the contact angle of the surface of the base material withrespect to pure water is less than 55 degrees.

5. The protective film for the polarizing plate described in claim 1wherein the contact angle of at least one surface of the protective filmfor the polarizing plate with respect to pure water is less than 55degrees.

6. The protective film for the polarizing plate described in claim 1wherein the surface of the base material is subjected to plasmatreatment.

7. The protective film for the polarizing plate described in claim 1,comprising a hydrophilic layer containing a hydrophilic high molecularcompound.

8. The protective film for the polarizing plate described in claim 1,wherein the base material is cellulose ester film, polycarbonate film,polyester film, or polyacryl film.

9. The protective film for the polarizing plate described in claim 1,wherein the average of the central line average roughness Ra of 10points on the surface of the protective film for the polarizing plate isbetween 1 and 80 nm, and the average of the maximum height differencesof 10 points arbitrary of said surface is between 5 and 80 nm.

10. A protective film for the polarizing plate, comprising a basematerial and an auxiliary layer, a protective film for the polarizingplate wherein in analysis of bonding state of carbon atom (C1s)employing X-ray photoelectron spectroscopy, when a peak having thelowest bonding energy is designated as a first peak, a peak positionedat 1.60±0.3 eV on the higher bonding energy side from the first peak isdesignated as a second peak, and a peak positioned at 4.10±0.3 eV on thehigher bonding energy side from the first peak is designated as a thirdpeak, bonding state of carbon atom C1s on a surface of at least one sideof the auxiliary layer and bonding state of internal carbon atom C1s ofthe auxiliary layer in an optional depth of 0.05 to 1 μm from thesurface satisfy relationship described below:S′−I′≧0.1

wherein S′ is intensity of the second peak on the auxiliary layersurface of the protective film for the polarizing plate/intensity of thefirst peak on the auxiliary layer surface of the protective film for thepolarizing plate, and I′ is intensity of the second peak in the interiorof the auxiliary layer of the protective film for the polarizingplate/intensity of the first peak of the interior of the auxiliary layerof the protective film for the polarizing plate.

11. A protective film for a polarizing plate, comprising a base materialwherein at least one surface of the base material is subjected to plasmatreatment.

12. A protective film for a polarizing plate, comprising a base materialand an auxiliary layer, wherein the surface of the auxiliary layer issubjected to plasma treatment.

13. A polarizing plate, comprising a first protective film, polarizerand a second protective film, wherein at least one of the firstprotective film and the second protective film comprises a basematerial, and in analysis of bonding state of a carbon atom employingX-ray photoelectron spectroscopy, when a peak having the lowest bondingenergy is designated as a first peak, a peak positioned at 1.60±0.3 eVon the higher bonding energy side from the first peak is designated as asecond peak, and a peak positioned at 4.10±0.3 eV on the higher bondingenergy side from the first peak is designated as a third peak, bondingstate of carbon atom C1s on the surface of at least one side of the basematerial and bonding state of internal carbon atom C1s in an optionaldepth of 0.05 to 1 μm from the surface satisfy relationship describedbelow:S−I≧0.1

wherein S is intensity of the second peak on the base material surfaceintensity of the first peak on the base material surface, and I isintensity of the second peak in the interior of the base materialintensity of the first peak of the interior of the base.

14. A liquid crystal display unit comprising a first polarizing plate, aliquid crystal cell, and a second polarizing plate provided in theinside of the first polarizing plate and the liquid crystal cell,wherein the first polarizing plate comprises

-   -   a first polarizer,    -   a first protective film provided to the surface of the first        polarizer on the side which does not face the liquid crystal        cell, and    -   a second protective film provided on the surface of the first        polarizer on the side which faces the liquid crystal cell;        the second polarizing plate comprises    -   a second polarizer,    -   a third protective film provided to the surface of the second        polarizer on the side which faces the liquid crystal cell, and    -   a fourth protective film provided to the surface of the second        polarizer on the side which does not face the liquid crystal        cell;        at least one of the first protective film, the second protective        film, the third protective film, and the fourth protective film        comprises a base material; and        in analysis of bonding state of a carbon atom (C1s) employing        X-ray photoelectron spectroscopy, when a peak having the lowest        bonding energy is designated as a first peak, a peak positioned        at 1.60±0.3 eV on the higher bonding energy side from the first        peak is designated as a second peak, and a peak positioned at        4.10±0.3 eV on the higher bonding energy side from the first        peak is designated as a third peak, bonding state of carbon atom        C1s on a surface of at least one side of the base material and        bonding state of internal carbon atom C1s in an optional depth        of 0.05 to 1 μm from the surface satisfy relationship described        below:        S−I≧0.1

wherein S is intensity of the second peak on the base material surfaceintensity of the first peak on the base material surface, and I is theintensity of the second peak in the interior of the base materialintensity of the first peak of the interior of the base.

15. A production method of a protective film for a polarizing plate,comprising the following steps, and a step in which a prepared film issubjected to plasma treatment.

16. The production method described in claim 15, wherein the plasmatreatment is a vacuum glow discharge, an atmospheric pressure glowdischarge, or a flame plasma treatment.

17. The production method described in claim 15 wherein the plasmatreatment is carried out a plurality of times.

18. The production method described in claim 15, wherein the plasmatreatment is subsequently or simultaneously carried out under theconditions in which the C—C bond or C—H bond of the organic substance onthe film surface is broken, or a hydroxyl group or amino group is formedon the film surface.

19. A production method of a polarizing plate comprising followingsteps:

a step in which the surface of a polarizer or a surface of a protectivefilm for the polarizing plate is subjected to plasma treatment, and

a step in which the protective film subjected to plasma treatment forthe polarizing plate is adhered with at least one of polarizer surfacesor a protective film for the polarizing plate is at least one ofpolarizer surfaces subjected to plasma treatment.

20. The production method described in claim 19, wherein after plasmatreatment and before adhering the protective film for the polarizingplate with a polarizer, the surface which has been subjected to plasmatreatment is washed with water.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing one example of an atmosphericpressure plasma treatment apparatus.

FIG. 2 is a cross-sectional view showing one example of an apparatuswhich carries out continuous vacuum plasma treatment.

FIG. 3 is an example of a plasma treatment apparatus employing a flame.

FIG. 4 is photoelectron spectra of a film.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will be detailed below.

Polarizing films are widely employed as liquid crystal display elementsin the display panel of desktop calculators, personal computers, liquidcrystal television sets, and displays in cars. As described above, suchpolarizing films have a structure in which a polarizer prepared byadsorbing and orienting iodine or dichroic dyes onto polyvinyl alcoholbased film is adhered with triacetyl cellulose film as the protectivefilm. The present inventors have investigated the following; theelimination of treatments which are not preferred in view of operationduring production of triacetyl cellulose film employed for saidprotective film, the protective film for the polarizing plate, whichexhibits excellent adhesion strength, and the production method of apolarizing plate which employs said protective film.

The present invention provides a novel method in which cellulose basedfilm is not subjected to conventional saponification during productionof a polarizing plate in which a protective film is adhered with apolarizer prepared by adsorbing and orienting iodine or dichroic dyesonto polyvinyl alcohol based film.

As described above, according to the present invention, it is possibleto obtain a film having excellent adhesive properties withoutsaponifying triacetyl cellulose film in strong alkali. Further, sincestrong alkali hydrolysis is not employed, it is possible to carry outhydrophilic treatment for the surface of triacetyl cellulose as well asother plastics.

In order to enhance the adhesive properties with a polyvinyl alcoholbased film employed in a polarizer, materials, which exhibit excellenthydrophilicity, are employed in the protective film for the polarizingplate.

The degree of hydrophilicity of a film surface is expressed by variousscales. However, it is convenient to express the degree employing acontact angle which is formed between a drop of water and the surfacewhen water is dropped.

The contact angle is commonly expressed by an angle, including liquidamong angles, between a tangential line drawn to the liquid and thesolid surface at the contact point of three phases when solid, liquid,and its saturated vapor come into contact. The contact angle closelyrelates to angle forming solid/surface tension of liquid as well assolid/liquid inter-facial tension. Thus, the contact angle is widelyutilized as the measure to express wettability of a solid surface withliquid. In the present invention, for the measurement of hydrophilicity,5 μl of pure water is placed on the surface of the protective film afterthe plasma treatment, and the contact angle between the water drop andthe protective film is measure at 23° C., employing a measurementapparatus (a goniometer Elmer G1, manufactured by Elmer Kogyo Co., Ltd.is employed). As the hydrophilicity rises, wettability with water isenhanced, and thus, the contact angle decreases. In the presentinvention, as the standard for the enhancement of hydrophilicity due tothe plasma treatment, it is required that the contact angle is 55° orless when it is measured by placing pure water on a protective filmsurface which faces a polarizer. Further, the contact angle with purewater is preferably between 0 and 50°, and is most preferably between 10and 40°. Under such conditions, the adhesive strength between thepolarizer film surface and the protective film increases and anexcellent polarizing plate may be obtained. Herein, pure water, Kind A4,specified in JIS K0557 is preferably employed.

Listed as resin films employed as the protective film for the polarizingplate of the present invention or its base materials may be, forexample, polyester films comprised of polyethylene terephthalate,polyethylene naphthalate, and the like, polyethylene film, polypropylenefilm, cellophane, films comprised of cellulose esters or derivativesthereof such as cellulose diacetate film, cellulose acetate butyratefilm, cellulose acetate phthalate film, cellulose acetate propionatefilm, cellulose triacetate, cellulose nitrate, polyvinylidene chloridefilm, polyvinyl alcohol film, ethylene vinyl alcohol film, syndioctaticpolystyrene based film, polycarbonate film, norbornane resin based film,polymethylpentene film, polyether ketone film, polyether sulfone film,polysulfone based film, polyether ketoneimide film, polyamide film,fluorine resin film, nylon film, polymethyl methacrylate film, acrylfilm, polyallylate based film, and the like. Films laminated with theseresins or films prepared by blending these resins may also be employed.

Other than acetyl cellulose based films (such as cellulose triacetate,cellulose diacetate, cellulose acetate butyrate, and the like),specifically, it is possible to preferably make the surface ofpolycarbonate, polyester film, polyacryl film, and the like,hydrophilic, employing the process instead of the aforementioned strongalkali treatment. Cellulose triacetate film, in which a thin cellulosediacetate layer is coat-provided on one surface or both surfaces, may bepreferably employed.

Further, if desired, it is possible to apply the plasma treatment to thecellulose ester film which has been subjected to alkali saponification,and further, to enhance its adhesive properties. Alternatively, film,which has been subjected to plasma treatment, may be subjected to alkalisaponification, and employed as the protective film for a polarizingplate.

On the other hand, by carrying out the plasma treatment instead of thealkali saponification, it is possible to enhance the adhesive propertieswithout varying the degree of substitution (the degree of acetylation ifa cellulose acetate based film is employed) on the surface of acellulose ester film.

The surface of the protective film for the polarizing plate, which isadhered with a polarizer, is preferably subjected to plasma treatmentprior to adhesion. Adhesion is preferably carried out within half a yearafter the plasma treatment, and is more preferably carried out withinone month. Most preferably, the plasma treatment is carried out severalhours or just before adhesion. Further, generally, effects due to theplasma treatment decrease during standing. However, it is discoveredthat washing improves the effects. Due to that, the protective film forthe polarizing plate, which has been subjected to plasma treatment, ispreferably immersed in water or warm water prior to adhesion.

Particularly improvement by washing is recognized in a film made ofpolyester such as polyethyleneterephthalate.

The protective film for the polarizing plate of the present inventionmay be comprised only of a base material, and may be comprised of saidbase material, an auxiliary layer and the like. Surface of the basematerial may be subjected to plasma treatment. After providing theauxiliary layer, its surface may be subjected to plasma treatment. Thecontact angle with respect to pure water on the base material surfacemay be below 55°. When an auxiliary layer is provided, the contact anglewith respect to pure water on the auxiliary layer surface may also bebelow 55°.

The auxiliary layer is not particularly limited. However, a hydrophiliclayer, an easily adhered layer, a fine particle containing layer, andthe like are preferred. The thickness of said auxiliary layer, such as ahydrophilic layer and the like, is preferably between 0.05 and 1 μm, andis more preferably between 0.1 and 1 μm.

Further, after dying and stretching, a polarizer treated with boric acidand the like occasionally exhibits insufficient adhesive properties withadhesives comprised of water-soluble polymers such as polyvinyl alcoholand the like. In order to overcome such a problem, variousinvestigations have been carried out. As a result, it has beendiscovered that after dying and stretching, a polarizer which has beentreated with boric acid and the like is subjected to plasma treatment,and subsequently, by adhering the resulting polarizer with theprotective film for the polarizing plate employing adhesives, adhesionof said polarizer with said protective film for the polarizing plate ismarkedly improved. Adhesives are preferably those comprised ofwater-soluble polymers such as polyvinyl alcohol and the like. Thus, ithas become possible to enhance the adhesive force by activating thepolarizer surface, which has been crosslinked, by boric acid treatment.More preferably, as described above, the protective film for thepolarizing plate is also subjected to plasma treatment.

In addition, the adhesive properties have been further improved byadjusting the roughness of the film surface so as to obtain a centralline average roughness Ra of 1 to 80 nm as well as maximum heightdifferences of 5 to 80 nm. It is possible to achieve such roughness bycarrying out the plasma treatment and to control the roughness byvarying the treatment conditions. Based on the plasma treatment, it ispossible to form unevenness having a larger cycle than saponification.Further, it is possible to obtain larger height difference, and thus toobtain the surface having an appropriate unevenness. The resultingunevenness is considered as one of the factors which improves adhesiveproperties.

The central line average roughness Ra was measured under a tapping mode,employing an inter-atomic force microscope, and at 10 optional places,the central line average roughness of a 0.5 μm straight line portion wasobtained. In this measurement, a surface shape was measured under adynamic mode (hereinafter referred to as DFM mode), employing a scanningtype probe microscope SPI3800N multifunctional type unit SPA400manufactured by Seiko Instruments. The employed cantilever was SI-DF20(made of silicone, having a spring constant of 20.0 N/m, a torsionspring constant of 100.0 N/m, a resonance frequency of 120 to 150 Hz, alever length of 200.0 μm, and a needle height of 3.00 μm). A sample wascut into about 1 cm cube, which was placed on the leveled sample standon a piezo scanner, and a cantilever was allowed to approach the samplesurface. When the cantilever reached a region in which an inter-atomicforce works, scan was carried out in the X and Y directions, and theunevenness of the sample was captured by piezo displacement in the Zdirection. The piezo scanner was employed which was capable of scanningX, Y 20 μm, and Z 2 μm. Scanning frequency was set at 1.00 Hz and ameasurement area was set at 0.5×0.5 μm. The number of data for X and Ywas 256 points, respectively. The obtained three-dimensional data werecorrected employing the first order gradient correction.

The central line average roughness Ra is preferably between 1 and 80 nmin terms of 10-point average, and is most preferably between 2 and 80nm. Further, the roughness Ra is preferably between 3 and 60 nm so thatexcellent adhesive properties are obtained. Further, the average ofmaximum height differences at 10 places in said length is preferablybetween 5 and 80 nm, is more preferably between 10 and 75 nm, and isfurther more preferably between 20 and 70 nm. When compared to thealkali saponification, Ra is larger, and the maximum height differenceis also larger. Such differences markedly contribute to enhancement ofthe adhesive properties. By applying the plasma treatment to theprotective film for the polarizing plate, it is possible to increase thenumber of hydroxyl groups, amino groups, carbonyl groups, carboxylgroups, and the like on said film. By so doing, wettability is improvedby lowering the contact angle, and further the adhesive properties areeffectively improved. Of groups, the hydroxyl group or the amino groupexhibits major effects to enhance the adhesive properties. In order toincrease the number of hydroxyl groups on the film surface, plasmatreatment is preferably carried out in an ambience comprising watervapor or water, oxygen, and the like. In order to increase the number ofamino groups, the plasma treatment is preferably carried out in anambience comprising at least ammonia or nitrogen, or further, watervapor or hydrogen. It is possible to examine those through surfaceanalysis, employing X-ray photoelectron spectroscopy.

After carrying out the plasma treatment under conditions in which theC—C bond or C—H bond of organic substances on the film surface isbroken, the plasma treatment is preferably carried out under conditionsin which hydroxyl groups or amino groups are formed on the film surface.By so doing, it is possible to introduce more hydroxyl groups or aminogroups and to obtain the film which exhibits better adhesive properties.Specifically, the plasma treatment is preferably carried out in thepresence of at least two types of gases selected from inert gases, suchas argon, neon, and the like, hydrogen, oxygen, ozone, water vapor,carbon dioxide, carbon monoxide, nitrogen, ammonia, nitrogen monoxide,nitrogen dioxide, lower hydrocarbons such as methane, ethane, and thelike, low boiling point organic compounds such as ketone, alcohol, andthe like.

It is possible to readily provide the same adhesive properties asobtained by saponification by carrying out the plasma treatment inreactive gases comprised of at least one type of gas selected from inertgases such as argon, neon, and the like, hydrogen, water vapor, hydrogenperoxide, and at least one type of gases selected from oxygen, watervapor, hydrogen peroxide, ozone.

Further, it was discovered that washing a plasma-treated film with waterfurther enhanced the adhesive properties. Thus, in another embodiment ofthe present invention, it is possible to produce a polarizing plate byadhering a film which is subjected to plasma treatment, and subsequentlyto water washing or warm water washing. As described above, waterwashing may be carried out successively after the plasma treatment, ormay be several hours to several months after the plasma treatment. Theeffects of the plasma treatment occasionally decrease during standing.However, since the effects are recovered by water washing, it ispreferably carried out just prior to adhering.

Further, the present invention is to provide a recycling method forpolarizing plates. Namely, cellulose acetate film, which is subjected toalkali saponification, is conventionally employed to produce polarizingplates. When the alkali saponification is applied, the ester bond on thesurface is subjected to hydrolysis. In recent years, the reuse andrecycling of source materials have been increasingly mandated. Regardingpolarizing plates, it is desired that film be separated from crushedplates, scrap, defective plates, and recovered plates, and the separatedfilm is then reused as a raw material for cellulose ester film. However,it has been found that when the conventional protective film employedfor the polarizing plate is reused, foreign matter increases and thequality of recycled products is degraded. The causes have beeninvestigated. As a result, it is assumed that the quality of recycledproducts is degraded due to inclusion of film in which esters on thesurface of cellulose ester film, which has been subjected to alkalisaponification, is hydrolyzed. Specifically, a cellulose ester filmsample is placed between two polarizing plates and the polarizing plateis arranged in cross Nicol. Then when one surface of the fabricatedsample is irradiated with light, light leaking spots (hereinafterreferred to as luminescent spot foreign particles) is observed. Thefewer the number of luminescent spot foreign particles, the morepreferred. However, it has been found that the protective film, which issubjected to saponification, is reused as a raw material for celluloseester, the number of said luminescent spot foreign particles tends toincrease, and the quality of the polarizing plate is degraded.

Some luminescent spot foreign particles comprised in acetylated cottonemployed as a raw material can be removed by filtration. However, it hasbeen difficult to remove luminescent spot foreign particles byfiltration which increase when cellulose ester film which is subjectedto saponification is employed as a raw material. On the other hand, whenthe cellulose ester film is not subjected to saponification, itsadhesive properties are insufficient. Due to that, problems occur duringcutting or handling, in which the protective film for the polarizingplate peels off from the polarizer. Consequently, the reuse of saidcellulose ester film has been diligently investigated. As a result, inanother embodiment of the present invention, it has been revealed thatcellulose ester film, which is specifically specified employinganalytical results of the carbon bonding state on the surface of theprotective film for the polarizing plate, is particularly preferable.

An XPS method (X-ray photoelectron spectroscopy) can be employed toinvestigate the bonding state of a carbon atom on the film surface andthe presence as a functional group. In order to precisely obtain thedifference in bonding state, it is preferred to employ a monochromaticAl X-ray source. Further, it is necessary to measure the bonding stateunder conditions in which when Ag 3d5/2 is measured employing a cleanedAg plate, its half band width is no more than 0.60 eV.

Spectra, which are employed to calculate the intensity of a peak, shouldbe subjected to sufficient integration so that of the three peaks ofC1s, the intensity of the maximum peak exceeds 15,000 counts. Further,it is necessary to space measured energy at interval of 0.05 eV, and tosufficiently control the peak shapes. Further, in order to clarify thedifference in peaks, it is necessary to control the energy resolution sothat when the peak of Ag 3d5/2 is measured employing a cleaned Ag plate,the half band with is no more than 0.6 eV.

When the surface of the corresponding protective film for the polarizingplate is measured employing the XPS method, C1s is obtained as spectrumhaving three peaks. In order to assign these peaks, as reference, forexample, “High Resolution XPS of Organic Polymer (The Scienta RSCA300Database, G. Beamson and D. Briggs)”, pages 164 and 165, and “APPENDIXX1.”

When a peak of the lowest bond energy is designated as a first peak, apeak positioned at 1.60±0.3 eV in the higher bond energy side from thefirst peak is designated a second peak, and a peak positioned at4.10±0.3 eV on the higher energy side from the first peak is designatedas a third peak, each peak can be assigned as shown in Table 1. PeakBonding State First Peak C—H and C—C bond Second Peak C—OH, C*—O—C, andC*—O—V═ O Third Peak C—O—C*═ O, HO—(C*═ O)—*expresses a subject carbon atom.

The bonding state of carbon atoms can be obtained by analyzing a C1speak due to the carbon atom measured by the X ray photoelectronspectroscopy. Namely, in XPS, the bonding state of carbon is analyzedthrough the measurement of the energy of a photoelectron released fromthe is orbital of the carbon atom.

The ratio of bonding states can be obtained employing the intensity ofeach peak. The intensity of the peak as described herein representscount number obtained by connecting with a straight line points on thebase line having the same bonding energy as the top from the top of eachpeak against the base line which is drawn between the energy value whichis 3 eV lower in the lower bond energy side forms the first peak and onewhich is 3 ev higher in the higher energy side from the third peak,employing a Shirley method.

The first peak emerges at 1.6±0.3 eV on the lower energy side withrespect to the second peak. However, when this part is not observed as apeak, the count number, obtained by connecting in a straight linebetween the intensity of the −1.6 eV part from the second peak and theaforementioned base line, is designated as the intensity of the firstpeak. The third peak emerges at 2.5±0.3 eV on the higher energy sidefrom the second peak. When the peak is observed, in the same manner, thecount number obtained by connecting in a straight line between the peaktop and the base line is designated as the intensity of the peak. Whenthe peak is not observed, the count number obtained by connecting instraight line between the intensity of +2.5 eV part on the higher energyside from the second peak and the aforementioned base line is designatedas the intensity of the third peak.

On the surface and in the interior of the film, it has been confirmedthat the more C—OH on the surface of the film, the better adhesion isobtained. Namely, in the of C1s peak analysis employing XPS, improvementof adhesion was observed by adjusting S-I specified by the followingformula to at least 0.10. S-I is more preferably at least 0.15, and isstill more preferably at least 0.20. S-I is preferably no more than 3.5,is more preferably no more than 2.5, and is still more preferably nomore than 1.5. By satisfying such conditions, when cellulose ester isemployed as a base material, it is possible to obtain a protective filmfor the polarizing plate which exhibits better recycling properties.S−I≧0.1

wherein S is the intensity of the second peak on the surface (or basematerial surface) of the protective film for the polarizing plate/theintensity of the first peak on the surface (or base material surface) ofthe protective film for the polarizing plate, and I is the intensity ofthe second peak in the interior (the interior of the base material orthe interior of the auxiliary layer) of the protective film for thepolarizing plate/the intensity of the first peak of the interior (theinterior of the base material or the interior of the auxiliary layer) ofthe protective film for the polarizing plate.

The interior of the base material as described herein means a placehaving an optimal depth in the range of 0.05 to 1 μm (preferably 0.2 to1 μm) from the base material surface. Further, the interior of theauxiliary layer as described herein means a place having an optimaldepth in the range of 0.05 to 1 μm from the surface thereof.

Said S is preferably at least 1.20, is more preferably at least 1.60 toobtain improved adhesion, and is still further preferably at least 1.70.It is most preferably at least 1.80 to obtain most improved adhesion.

Further, the ratio of relative intensity of C1s peak, which is expressedby T, that is, the third peak intensity of the surface (or the basematerial surface) of the protective film for the polarizing plate/thesecond peak intensity of the surface (or the base material surface) ofthe protective film for the polarizing plate, is preferably at least2.0, is more preferably at least 0.4, and is most preferably at least0.6. When such cellulose ester is employed, it has been found that theluminescent spot foreign particles preferably decrease.

Further, it is preferable to satisfy the following formula.T−U>0

wherein U is the intensity of the third peak in the interior of 10 μmfrom the base material surface/the intensity of the second peak in theinterior of 10 μm from the base material surface.

The film surface as described herein means a region having a depth ofabout 200 angstrom form the surface, which is measured by XPS. Theinterior means the region which is more than said depth from thesurface. In order to measure the interior, the region having a thicknessof more than said depth is shaved off, and a newly exposed surface canbe measured.

It is preferable that the number of hydroxyl groups, which bond to acarbon atom on the base material surface or in the surface of theauxiliary layer, is more than that the number of hydroxyl groups whichbond to a carbon atom in the interior of the base material or theauxiliary layer. It is also preferable that the number of amino groups,which bond to a carbon atom on the base material surface or the interiorof the auxiliary layer, is more than the number of amino groups whichbond to a carbon atom in the interior of the base material or theauxiliary layer. Furthermore, it is preferable that the total number ofhydroxyl groups and amino groups, which bond to a carbon atom on thebase material surface or the interior of the auxiliary layer, is morethan that the total number of hydroxyl groups and amino groups whichbond to a carbon atom in the interior of the base material or theauxiliary layer.

Specifically, such cellulose ester film is obtained employing the plasmatreatment instead of the saponification. Namely, the plasma treatmenthardly varies the degree of substitution of esters on the surface.Namely when the plasma treatment is applied, the degree of estersubstitution is hardly varied. Thus, it has become possible topreferably reuse scrap as well as cut waste of cellulose ester film,which has been subjected to plasma treatment instead of saponification,and scrap and waste of cellulose ester film separated from polarizingplates using the same, as the raw material of cellulose ester film.

Accordingly, based on said method, it is possible to reuse as a rawmaterial the cellulose ester film which has been subjected to plasmatreatment and to produce recycled cellulose ester film. If desired,cellulose ester powder as a raw material and cellulose ester film, whichhas been subjected to plasma treatment, may be blended in an optionalratio and employed. At that time, a small amount of cellulose esterfilm, which has been subjected to saponification, may be blended with araw material. However, it is preferable that no cellulose ester film,which has been subjected to saponification, is contained.

The recycled cellulose ester film, as described above, may preferablyemployed not only as the protective film for the polarizing plate butalso as films for other optical use or supports for photosensitivematerials.

Cellulose ester film according to the present invention is preferablycomprised of cellulose esters which are lower fatty acid esters. Thelower fatty acid in the lower fatty acid ester of the cellulose ester asdescribed herein means a fatty acid having from 1 to 5 carbon atoms.Cited as examples of preferable lower fatty acid esters are cellulosediacetate, cellulose triacetate, cellulose propionate, cellulosebutyrate, and the like. These may be employed in combination of twotypes or more.

Further, other than those described above, mixed fatty acid esters suchas cellulose acetate propionate, cellulose acetate butyrate, and thelike may be employed, which are described in Japanese Patent PublicationOpen to Public Inspection Nos. 10-45804, and 08-231761, and U.S. Pat.No. 2,319,052, and others.

These cellulose esters may be employed individually or in combination.

Of these described above, lower fatty acid esters of cellulose which aremost preferably employed include cellulose triacetate, cellulosepropionate or mixtures thereof.

Further, from the viewpoint of base strength, those particularly havinga degree of polymerization of 250 to 400 as well as a combined aceticacid amount of 54 to 62.5 percent are preferably employed. Cellulosetriacetate having a combined acetic acid amount of 58 to 62.5 percent ismore preferably employed.

There are two types of cellulose triacetate, i.e. cellulose triacetatemade from linter and cellulose triacetate made from wood pulp. These arepreferably employed individually or in combination. When problems withpeeling properties from a belt as well as a drum occur, the ratio of thecellulose triacetate made from linter, which exhibits good peelingproperties, may preferably be increased so that the productivityincreases.

When cellulose triacetate made from wood pulp is blended with cellulosetriacetate made from linter and employed, the ratio of said cellulosetriacetate is preferably at least 40 percent by weight so as to obtainmarked effects to improve peeling properties, is more preferably atleast 60 percent by weight, is still more preferably at least 85 percentby weight, and is most preferably 100 percent by weight.

In order to improve slipping properties, fine particles may beincorporated into the protective film for the polarizing plate of thepresent invention. Listed as fine particles are inorganic compounds ororganic compounds.

Preferred as inorganic compounds are silicon-containing compounds,silicon dioxide, aluminum oxide, zirconium oxide, calcium carbonate,talc, sintered kaolin, sintered calcium silicate, hydrated calciumsilicate, aluminum silicate, magnesium silicate, calcium phosphate, andthe like. Of these, inorganic silicon-containing compounds and zirconiumoxide are more preferred. Silicon dioxide is most preferably employedbecause the turbidity of cellulose ester film can be reduced.

Employed as fine particles of silicon dioxide may be, for example,commercially available products having a trade name such as AerojiruR972, R974, R812, 200, 300, R202, OX50, and TT600 (these aremanufactured by Nihon Aerojiru Co., Ltd.).

Employed as fine zirconium oxide particles may be, for example,commercially available products having a trade name such as AerojiruR976 and R811 (these are manufactured by Nihon Aerojiru Co., Ltd).

Preferably employed as organic compounds may be, for example, polymerssuch as silicone resins, fluorine resins, acrylic resins, and the like.Of these, silicone resins are preferably employed.

Of silicone resins described above, those having a three-dimensionalstructure are preferred. Commercially available products having a tradename of Tospearl 103, same 105, same 108, same 120, same 145, same 3120and same 240 (these are manufactured by Toshiba Silicone Co., Ltd.) maybe employed.

From the viewpoint to control haze to the lower level, the averageprimary particle diameter of fine particles is preferably no more than20 nm, is more preferably between 5 and 16 nm, and is most preferablybetween 5 and 12 nm.

The average primary particle diameter of fine particles was measured asfollows: 100 particles were observed employing an emission type electronmicroscope (at a magnifying factor of 500,000 to 200,000,000), and theresulting average value was denoted as the average primary particlediameter.

The apparent specific gravity of fine particles is preferably at least70 g/liter, is more preferably between 90 and 200 g/liter, and is mostpreferably between 100 and 200 g/liter. When the apparent specificgravity increases, it is possible to prepare a dispersion having ahigher concentration. Thus the haze as well as coagula is preferablydecreased.

Fine silicon dioxide particles, having an average primary particlediameter of, mo more than 20 nm as well as an apparent specific gravityof at least 70 g/liter, is obtained, for example, by combusting amixture consisting of vaporized silicon tetrachloride and hydrogen at1,000 to 1,200° C. in air. Further, products having a trade name ofAerojiru 200V and Aerojiru R972V (these are manufactured by NihonAerojiru Co., Ltd.) may be employed, which are available on the market.

In the present invention, the apparent specific gravity described abovewas calculated by the formula described below, while a definite amountof fine silicon dioxide particles were placed in a measuring cylinderand then the resulting weight was measured.Apparent specific gravity (in g/liter)=(weight of silicon dioxide (ing)/volume of silicon dioxide (in liter)

Listed as methods to prepare fine particle dispersions are the threetypes described below:

(Preparation Method A)

After blending while stirring a solvent with fine particles, theresulting mixture is subjected to dispersion employing a homogenizer.The resulting dispersion is designated as a fine particle dispersion.Said fine particle dispersion is added to a dope and stirred.

(Preparation Method B)

After blending with stirring a solvent with fine particles, theresulting mixture is subjected to dispersion employing a homogenizer.The resulting dispersion is designated as a fine particle dispersion.Separately, a small amount of cellulose acetate is added to a solvent,mixed and dissolved. Said fine particle dispersion is added to theresulting cellulose acetate solution and stirred. The mixture isdesignated as a fine particle addition composition. Said fine particleaddition composition is well mixed with a dope employing a in-linemixer.

(Preparation Method C)

A small amount of cellulose acetate is added to a solvent, stirred, anddissolved. Fine particles are added to the resulting cellulose acetatesolution and dispersed employing a homogenizer. The resulting dispersionis designated as a fine particle addition composition. The resultingfine particle addition composition is well mixed with a dope employingan in-line mixer.

Preparation Method A is excellent in efficient dispersion of finesilicon dioxide particles, and Preparation Method C is excellent inminimization of re-coagulation of fine silicon dioxide particles.Preparation Method B is excellent in both efficient dispersion of finesilicon dioxide particles as well as minimization of re-coagulation offine silicon oxide particles, and thus is a preferable preparationmethod.

(Dispersion Method)

When fine silicon dioxide particles are mixed with solvents and the likeand dispersed, the concentration of said silicon dioxide is preferablybetween 5 and 30 percent by weight, is more preferably between 10 and 20percent by weight, and is most preferably between 15 and 20 percent byweight. When the dispersion concentration increases, the turbidity withrespect to the added amount tends to decrease. Thus such increase ispreferred to decrease the haze as well as the coagula.

Listed as employed solvents are lower alcohols, preferably such asmethyl alcohol, ethyl alcohol, propyl alcohol, isopropyl alcohol, butylalcohol, and the like. As solvents other than lower alcohols, solvents,which are employed for casting cellulose esters, are preferablyemployed.

The added amount of fine silicon dioxide particles with respect tocellulose ester is preferably between 0.01 and 0.3 weight part per 100weight parts of cellulose ester, is more preferably between 0.05 and 0.3weight part, and is most preferably between 0.08 and 0.12 weight part.When the added amount is larger, dynamic friction coefficient isimproved, while the added amount is less, the haze as well as coaguladecreases.

Ordinary homogenizers may be employed. Homogenizers are mainly dividedinto two types; a media homogenizer and a medialess homogenizer. Finesilicon dioxide particles are preferably dispersed by the medialesshomogenizer which results in decrease in haze.

Cited as medialess homogenizers are a ball mill, a sand mill, a dynomill, and the like.

As medialess homogenizers, there are an ultrasonic type, a centrifugaltype, a high pressure type, and the like. In the present invention, thehigh pressure type homogenizer is preferred. The high pressurehomogenizer is an device which generates special conditions such as highshearing, high pressure, and the like by passing a composition preparedby mixing fine particles with solvents into a narrow pipe at a highspeed. For example, in a narrow pipe having a diameter of 1 to 2,000 μm,the maximum pressure in the interior of a device is preferably at least9.8 Mpa. Further, at the time, a device that allows a maximum attainablespeed to exceed 100 m/second, as well as heat transfer rate to exceed420 kJ/hour is preferred.

Ultra-high pressure homogenizers as described above include anultra-high pressure homogenizer (with a trade name of Microfluidizer)manufactured by Microfluidics Corporation, and Nanomizer manufactured byNanomizer Co. Listed as devices other than those are Manton-Gaulin typehigh pressure homogenizer, for example, Homogenizer manufactured byIzumi Food Machinery, UHN-01 manufactured by Sanwa Kikai Co., Ltd., andthe like.

In the protective film of the present invention, an auxiliary layer maybe provided on a base body. Said auxiliary layer comprises a layercontaining fine particles, a layer containing hydrophilic high molecularcompounds, an readily adhesive layer, and the like. Further, in order toimprove the slipping properties, it is preferable that a layercomprising fine particles according to the present invention is cast soas to come in direct contact with a casting support.

UV absorbers, which relate to the cellulose ester film of the presentinvention, will be described.

The cellulose ester film of the present invention exhibits highdimensional stability. Therefore, it is employed in polarizing plates,liquid crystal display members, and the like. From the viewpoint toprevent degradation of said polarizing plates, liquid crystals, and thelike, UV absorbers are preferably employed.

Preferably employed as UV absorbers are those, which well absorbultraviolet rays having a wavelength of no longer than 370 nm and absorbminimal visible light having a wavelength of no shorter than 400 nm.

Listed as specific examples preferably employed in the present inventionare oxybenzophenone based compounds, benzotriazole based compounds,salicylic ester based compounds, benzophenone based compounds, cyanoacrylate based compounds, nickel complex based compounds, and the like.

As benzotriazole based UV absorbers, the compounds represented by thefollowing general formula (I) are preferably employed.

wherein R₁, R₂, R₃, R₄, and R₅ may be the same or different, and eachrepresents a hydrogen atom, a halogen atom, a nitro group, a hydroxylgroup, an alkyl group, an alkenyl group, an aryl group, an alkoxy group,an acyloxy group, an aryloxy group, an alkylthio group, an arylthiogroup, a mono- or dialkylamino group, an acylamino group, a 5- or6-membered heterocyclic group, and R₄ and R₅ may form 5- or 6-memberedcarbon ring by closing a ring.

Specific examples of UV absorbers represented by the general formula (I)are shown below:

-   UV-1: 2-(2′-hydroxy-5′-methylphenyl)benzotriazole-   UV-2: 2-(2′-hydroxy-3′,5′-di-tert-butylphenyl)benzotriazole-   UV:3: 2-(2′-hydroxy-3′-tert-butyl-5′-methylphenyl)benzotriazole-   UV-4: 2-(2′-hydroxy-3′,5′-di-tert-butylphenyl)-5-chlorobenzotriazole-   UV-5:    2-(2′-hydroxy-3′-(3″4″,5″,6″-tetrahydrophthalimidomethyl)-5′-methylphenyl)benzotriazole-   UV-6:    2,2-methylenebis(4-(1,1,3,3-tetramethylbutyl)-6-(2H-benzotriazole-2-yl)phenol)-   UV-7:    2-(2′hydroxy-3′-tert-butyl-5′-methylphenyl)-5-chlorobenzotriazole

Further, preferably employed as benzophenone based UV absorbers, whichare one type of UV absorbers related to the present invention, arecompounds represented by the general formula (II):

wherein Y represents a hydrogen atom, a halogen atom, an alkyl group, analkenyl group, an alkoxy group, and a phenyl group which may have asubstituent, A represents a hydrogen atom, an alkyl group, an alkenylgroup, a phenyl group, a cycloalkyl group, an alkylcarbonyl group, analkenylsulfonyl group, or —CO(NH)_(n-1)-D group, wherein D represents analkyl group, an alkenyl group, or a substituted or unsubstituted phenylgroup, and m and n each represents 1 or 2.

In foregoing, the alkyl group is for example, a straight or branchedaliphatic group having from 1 to 24 carbon atoms, the alkoxy group is,for example, an alkoxy group having from 1 to 18 carbon atoms, thealkenyl group is, for example, an alkenyl group having from 1 to 16carbon atoms, and represents an allyl group, an 2-butenyl group, and thelike. Listed as substituents on an alkyl group, an alkenyl group, anphenyl, group are a halogen atom such as a chlorine atom, a bromineatom, a fluorine atom, a hydroxyl group, a phenyl group (this phenylgroup may be substituted with an alkyl group, a halogen atom, and thelike).

Specific examples of benzophenone based compounds represented by thegeneral formula (II) are shown below:

-   UV-8: 2,4-dihydroxybenzophenone-   UV-9: 2,2′-dihydroxy-4-methoxybenzophenone-   UV-10: 2-hydroxy-4-methoxy-5-sulfobenzophenone-   UV-11: bis(2-methoxy-4-hydroxy-5-benzoylphenylmethane

UV absorbers, described in Japanese Patent Publication Open to PublicInspection No. 6-148430, may also be preferably employed.

UV absorbers described above, which are preferably employed in thepresent invention, exhibit excellent transparency, as well as excellenteffects to minimize the degradation of polarizing plates as well asliquid crystal elements. Of them, benzotriazole based UV absorbers arepreferred which specifically have minimal unnecessary tint. Additionmethods of the addition composition comprising these UV absorbersinclude the following:

(Addition Method A)

A UV absorber addition composition is prepared by dissolving UVabsorbers in an organic solvent such as alcohol, methylene chloride,dioxolane, and the like. the resulting solution is directly added to adope composition.

(Addition Method B)

A UV absorber addition composition is prepared by dissolving UVabsorbers together with a small amount of cellulose ester in an organicsolvent such as alcohol, methylene chloride, dioxolane, and the like.The resulting solution is added to a dope employing an in-line mixer.

Addition Method B is more preferred because the addition amount of UVabsorbers can readily be controlled, and thus productivity is enhanced.

The employed amount of UV absorbers varies depending on the type ofcompounds, employed conditions, and the like. However, said amount ispreferably between 0.2 and 5.0 g per m² of cellulose ester film, is morepreferably between 0.4 and 1.5 g, and is most preferably between 0.6 and1.0 g.

The thickness of the cellulose ester film of the present invention willnow be described.

When the total thickness of cellulose ester film is excessively small,toughness as the protective layer for the polarizing plate becomesinefficient to degrade the dimensional stability of the polarizing plateas well as the keeping stability thereof against moisture and heat. Whenthe thickness is excessively large, the polarizing plate becomesthicker, and it is difficult to reduce the thickness of a liquid crystaldisplay. The thickness of the layer of cellulose ester laminated film,which overcomes those problems is between 20 and 200 μm, is preferablybetween 30 and 100 μm, and is more preferably between 40 and 80 μm.

The production method of cellulose eater film will be described.

In order to produce cellulose ester film, the following method isemployed: first, cellulose ester is dissolved in a solvent and a dope isprepared, and the resulting dope is cast on an endless belt, peeled off,and subsequently dried.

The dope, in which cellulose ester is dissolved, is in a state in whichsaid cellulose is dissolved in a solvent. Additives such as plasticizersand the like may be incorporated into said dope. Needless to say, ifrequired, other additives may be incorporated. The concentration ofcellulose ester in said dope is preferably between 10 and 30 percent byweight, and is more preferably between 18 and 25 percent by weight.

Solvents in the present invention may be employed individually or incombination. However, from the viewpoint of production efficiency, it ispreferable that good solvents and bad solvents are mixed and employed.The mixing ratio of the good solvent to the bad solvent is preferablybetween 70 and 95 percent by weight, while said ratio of the bad solventto the good solvent is preferably between 5 and 30 percent by weight.

Good solvents and bad solvents which are employed in the presentinvention are defined as follows: the solvent itself, which dissolvesemployed cellulose ester, is a good solvent, while the solvent itselfwhich neither swells nor dissolves said cellulose ester is a badsolvent. Due to that, depending on the amount of acetic acid which iscombined with cellulose ester, a bad solvent varies to a good solvent.For example, when acetone is employed as the solvent, it is a goodsolvent for cellulose ester in which the amount of combined acetic acidis 55 percent, while it is a bad solvent for cellulose ester in whichthe amount of combined acetic acid is 60 percent.

Listed as good solvents employed in the present invention are organichalogen compounds such as methylene chloride and the like anddioxolanes.

Further, preferably employed as bad solvents employed in the presentinvention are, for example, methanol, ethanol, n-butanol, cyclohexane,and the like.

When the aforementioned dope is prepared, a common method may beemployed to dissolve cellulose ester. A preferred method is such thatsaid cellulose ester is mixed with bad solvents so that it is damped andswelled, and further mixed with good solvents. At the time, theresulting mixture is preferably heated under increased pressure in therange of temperature at which solvents boil at normal temperature and donot boil, and said cellulose ester is dissolved while stirring in orderto minimize the formation of gel as well as insoluble coagula.

Pressure may be raised by introducing inert gases such as nitrogen gas,or by the increase in vapor pressure by heating. Heating is preferablycarried out from the exterior. For example, a jacket type is preferred,since the temperature is readily controlled.

Further, a dope is preferably employed which is prepared by employing afreeze dissolution method in which without employing halogen basedsolvents, cellulose esters such as cellulose triacetate and the like arecooled below −20° C. together with methyl acetate and/or solvent such asacetone, methyl acetate and ethanol, and the like and thereafter, areheated.

In the present invention, during preparation of said dope, scrap and thelike of cellulose ester, which has been subjected to plasma treatment,may be employed as the raw material of cellulose ester or a part of saidraw material.

When solvents are added, heating temperature is set in the range of thelower temperature than the boiling point of the employed solvent to thetemperature at which said solvent does not boil, and is preferably set,for example, in the range of 60 or 70 to 110° C. Further, the pressureis controlled so that said solvent does not boil at a set temperature.The solvent can be controlled not to boil at temperature higher than theboiling point under normal pressure by adding higher pressure.

After cellulose ester is dissolved, the dissolved cellulose ester isremoved from the vessel or is removed from the vessel employing a pumpand cooled employing a heat exchanger, and employed for casting. At thetime, said dissolved cellulose ester may be cooled to normaltemperature. However, when it is cooled to the temperature at 5 to 10°C. lower than the boiling point of the solvent, and is preferablysubjected to casting without varying the temperature so that theviscosity of the dope can be decreased.

During a casting process, a belt-shaped support or a drum-shaped supporthaving a secular finished stainless steel surface is preferablyemployed. Casting may be carried out on the support maintained at thecommon temperature range of 0° C. to below the boiling point of theemployed solvent. However, casting is preferably carried out on thesupport which is maintained at 0 to 35° C. so that the dope is gelledand the peel limit time can be shortened. The casting is more preferablycarried out on the support maintained at 5 to 20° C. The peel limit timeas described herein means a time of the cast dope on the support in thelimit of the casting speed which makes it possible to continually obtaina transparent film with excellent flatness. The shorter peel limit timeis preferred so that productivity is enhanced.

The temperature of the support surface, on which the dope is cast, isbetween 10 and 55° C., and the temperature of the dope is between 25 and60° C. Further, the temperature of the dope is preferably higher thanthe support, and is more preferably at least 5° C. higher. Thetemperature of the dope as well as the support is preferably as high aspossible to increase the vaporization rate of solvents. However, when itis excessively high, occasionally air bubbles are generated and theflatness is degraded.

The temperature of the support is more preferably in the range of 20 to40° C., and the temperature of the dope is more preferably in the rangeof 35 to 45° C.

Further, the support temperature of the peeling section is preferablybetween 10 and 40° C., and is more preferably between 15 and 30° C. sothat adhesive force between the film and support can be decreased to bereadily peeled off.

In order to obtain excellent flatness of cellulose ester film duringproduction, the amount of residual solvents at peeling is preferablybetween 10 and 100 percent, is more preferably between 20 and 40 percentor between 60 to 80 percent, and is most preferably between 20 and 30percent.

In the present invention, the amount of residual solvent is defined bythe following formula:Amount of residual solvent (in %)=(weight prior to heatingprocess−weight after heating process)/(weight after heating process)×100

Further, the heating process during measurement of the amount of theresidual solvent means a heating process in which a film is heated at115° C. for one hour.

Peeling tension during peeling of a film from a support is commonlybetween 200 and 250 M/m. However, when the cellulose ester film whichcomprises a higher content of UV absorbers per unit weight of thecellulose ester and has a less thickness than conventional one,wrinkling tends to result during peeling. Therefore, peeling ispreferably carried out at the lowest tension of 170 N/m, and is morepreferably carried out at the lowest tension of 140 N/m at which thefilm is capable of being peeled.

Further, in the drying process of cellulose ester film, the film peeledfrom the support is further dried. At that time, the residual solventcontent is preferably reduced to no more than 3 percent by weight and ismore preferably reduced to no more than 0.5 percent by weight.

In the drying process, film is preferably dried, while commonlyconveying said film employing a roll loft method or a pin tenter method.For a liquid crystal display member, a film is preferably dried whilemaintaining the width employing the pin tenter method so that thedimensional stability is improved. Maintaining the width immediatelyafter peeling from the support, while the residual solvent content ishigh, is particularly preferred because the improvement effect ofdimensional stability is further exhibited. Film drying means are notparticularly limited, and generally drying is carried out employingheated air flow, infrared rays, heated rolls, microwave, and the like.Heated airflow is preferably employed due to its convenience. Dryingtemperatures are suggested to be in the range 40 to 150° C., and dryingis preferably carried out while dividing the temperature to 3 to 5levels which are gradually raised. Drying is more preferably carried outin the range of 80 to 140° C. so that the dimensional stability isenhanced.

Further, if desired, cellulose ester film, having a laminated structure,may also be employed, which is prepared by co-casting a plurality ofdoping materials.

The co-casting as described herein includes a successive multilayercasting method in which two or three layers are formed through differentdies, a simultaneous multilayer casting method in which two or threelayers are formed by combining layers in a die having two or threeslits, a successive casting method, and the like. Of these, thesimultaneous multilayer casting method is preferred due to its highproductivity. Examples of production of laminated film employing theco-casting are, for example, described in Japanese Patent PublicationOpen to Public Inspection Nos. 10-235664 and 11-216732.

Plasticizers are preferably incorporated into the cellulose ester filmof the present invention. Employable plasticizers include phosphoricacid esters such as triphenyl phosphate, tricresyl phosphate, cresyldiphenyl phosphate, octyl diphenyl phosphate, diphenyl biphenylphosphate, trioctyl phosphate, tributyl phosphate, and the like;phthalic acid esters such as diethyl phthalate, dimethoxyethylphthalate, dimethyl phthalate, dioctyl phthalate, dibutyl phthalate,di-2-ethylhexyl phthalate, and the like; glycolic acid esters such astriacetin, tributin, butylphtharylbutyl glycolate, ethylphtharylethylglycolate, methylphtharylethyl glucolate, butylphtharylbutyl glucolate,and the like. These may be employed individually or in combination. Aphosphoric acid based plasticizer is most preferably employed togetherwith a plasticizer having a solidifying point of no more than 20° C. toimprove dimensional stability as well as water resistance. Plasticizershaving a solidifying point of no more than 20° C. can be selected fromthose listed above which have a solidifying point of no more than 20° C.Specifically listed are tricresyl phosphate, cresyldiphenyl phosphate,tributyl phosphate, diethyl phthalate, dimethyl phthalate, dioctylphthalate, dibutyl phthalate, di-2-ethylhexyl phthalate, triacetin,ethylphtharylethyl glycolate, and the like. These plasticizers may beemployed individually or in combination.

The solidifying point as described herein means a true solidifying pointas described in “Kagaku Daijiten (Chemical Encyclopedia)” published byKyoritsu Shuppan Co., Ltd.

These plasticizers may be added up to about 30 percent by weight withrespect to cellulose ester, depending on film performance,machininability, and the like. However, the added amount is preferablybetween 1 and 15 percent by weight. For the member of the liquid crystaldisplay, the added amount is preferably between 5 and 15 percent byweight from the viewpoint of dimensional stability, and is mostpreferably between 7 and 12 percent by weight. Further, the content ofplasticizers having a solidifying point of no more than 20° C. ispreferably between 1 and 10 percent by weight with respect to celluloseester, and is more preferably between 3 and 7 percent by weight.

A larger ratio of plasticizers having a solidifying point of no morethan 20° C. to the total plasticizers is preferred, since theflexibility as well as machinability of cellulose ester film isimproved. Further, plasticizers are most preferably comprised of thosehaving a solidifying point of no more than 20° C.

The average content of plasticizers within the range of 10 μm from thesurface, which is subjected to plasma treatment, is preferably less interms of adhesive properties. Said content with respect to the averagecontent of plasticizers in the entire film is preferably no more than ¾,and is most preferably between 1/10 and ¾.

Listed as the plasma treatment employed in the present invention are avacuum glow discharge, an atmospheric pressure glow discharge, and thelike. A flame plasma treatment and the like are listed as other methods.For these, employed may be methods described, for example, in JapanesePatent Publication Open to Public Inspection Nos. 6-123062, 11-293011,11-5857 and others.

By employing the plasma treatment, it is possible to provide stronghydrophilicity to the surface of plastic which is placed in plasma. Forexample, in a plasma generating apparatus employing the aforementionedglow discharge, a film to be subjected to hydrophilicity is placedbetween facing electrodes, and plasma excitation gas is introduced intosaid apparatus. Then by applying high frequency voltage to bothelectrodes, it is possible to carry out surface treatment by plasmaexcitation said gas and generating a glow discharge between saidelectrodes. Of these, the plasma treatment employing the atmosphericpressure glow discharge is preferably employed.

The plasma excitation gas as described herein means a gas which issubjected to plasma excitation in the aforementioned conditions, andincludes argon, helium, neon, krypton, xenon nitrogen, carbon dioxide,flons such as tetrafluoromethane, and mixtures thereof.

A mixture of inert gas such as argon, neon, and the like with a reactivegas, which is capable of providing a polar functional group such as acarboxyl group, a hydroxyl group, a carbonyl group, and the like ontothe plastic surface, is employed as the excitation gas. Other thanhydrogen, oxygen, and nitrogen, if required, employed as reactive gasesmay be gases such as water vapor, ammonia, and the like, and further lowboiling point organic compounds such as lower hydrocarbons, ketones, andthe like. However, due to ease of handling, hydrogen, oxygen, carbondioxide, nitrogen, water vapor and the like are preferred. When watervapor is employed, gas, which is bubbled in water, may be employed.Alternatively, a gas may be mixed with water vapor.

The employed frequency of applied high frequency voltage is preferablybetween 1 and 100 kHz, and is more preferably between 1 and 10 kHz.

There are two methods of the plasma treatment employing the glowdischarge; one in a vacuum and the other under atmospheric pressure.

In the vacuum plasma discharge treatment employing the glow discharge,in order to effectively generate said discharge, it is required tointroduce the aforementioned reactive gas so as to maintain the ambientpressure in the range of 0.005 to 20 torr. In order to increase thetreatment rate, it is preferred to employ high output conditions on thehigh pressure side. However, when the electric field strength isexcessively increased, the base material occasionally suffers fromdamage.

When the atmospheric pressure glow discharge, which carries out theplasma discharge at the pressure near atmospheric pressure, is employed,in order to generate a stable discharge, inert gases such as helium,argon, and the like are required. Thus, when the aforementionedexcitation gases contain inert gases in an amount of at least 60percent, stable discharge is generated. However, when the ratio of theinert gases is excessively high and the ratio of the reactive gases islow, the treatment rate decreases. When the electric field strength isexcessively increased, damage to the base material occasionally results.

Further, when the plasma treatment is carried out at pressure nearatmospheric pressure, said inert gases are not always required togenerate pulsed electrochemical plasma. Accordingly, it is possible toincrease the concentration of the reactive gases to increase thereaction rate.

In the flame plasma treatment, the plasma is generated by carrying out aflame treatment on the surface of the film to be subjected to surfacetreatment, and the surface treatment is carried out employing theresultant plasma. For example combustion gasses such as paraffin basedgases city gas, natural gas, methane gas, propane gas, butane gas, andthe like) are mixed with oxidizing gases such as air and oxygen (orcombustion aids, oxidizing agents and the like are occasionallyemployed). The resulting mixture is combusted and the surface issubjected to treatment employing the resulting flame.

Generally, a flame generated from a burner is composed of an inner flameand an exterior flame. The exterior flame is a part composed of the gasof the inner flame which is not combusted and heated, and commonly ispale blue. Thus the exterior flame is a so-called blue gas flame, and apart having a relatively high temperature. The part of the flame whichis not blue is the inner flame and has a relatively low temperature dueto the low supply of oxygen.

Within 30 mm from the top of the inner flame, a large amount of plasmais generated. As described in Japanese Patent Publication Open to PublicInspection No. 11-184042, by regulating the flame using a shieldingplate, it is possible to treat a base material surface employing theflame which is limited from the top to 30 mm. Accordingly, by employingsuch a flame, it is possible to carry out the plasma treatment.

The duration of flame application is between 0.001 and 2 seconds, whilethe flame is brought into contact with the base material to be treated.The duration is preferably between 0.01 and 1 second. When the time isexcessively long, the surface is subjected to excessive treatment, whilewhen the time is shorter, only slight oxidation reaction occurs and theadhesive properties are not improved.

The burner, which is employed for this purpose, is not particularlylimited as long as it is capable of providing a uniform flame on thebase material surface to be treated. Further, a plurality of burners maybe arranged.

The mixing ratio of the combustion gas to the oxidizing gas employed inthe aforementioned flame treatment varies depending on the type ofgases. For example, in the case of propane gas and air, the volume ratiois preferably in the range of 1/15 to 1/22, and is more preferably inthe range of 1/16 to 1/19. In the case of natural gas and air, thevolume ratio is preferably in the range of 1/6 to 1/10, and is morepreferably in the range of 1/7 to 1/9. The size ratio of the inner flameto the exterior flame varies depending on the types of combustion gases,the types of oxidizing gases, the mixing ratio, the supplying rate, andthe like.

In FIG. 1, an atmospheric plasma treatment apparatus is shown as anexample of a plasma treatment apparatus. In FIG. 2, an apparatus isshown in which a continuous vacuum plasma treatment is carried out.

FIG. 1 is a cross-sectional view showing an example of an atmosphericpressure plasma treatment apparatus. Namely, in the atmospheric pressureplasma generating apparatus in FIG. 1, between two facing electrodes(upper and lower electrodes are represented by reference numeral 1),sample 2 is placed which is to be subjected to plasma treatment. Inorder to prevent spark discharge during plasma excitation, dielectric 3such as glass, ceramics, and polyimide film is preferably provided onthe surface of said upper and/or lower electrode. A plasma excitationgas such as a gas mixture of argon and helium is introduced into theatmospheric pressure plasma generating apparatus from inlet 4, andreplaces the inner air and is then ejected from an outlet. Subsequently,high frequency voltage, for example, 3000 Hz and 4,200 V is applied tothe electrodes, said introduced gas is subjected to plasma excitation,and a glow discharge is generated for a specified time. Thus, the samplesurface is subjected to modification.

FIG. 2 is a cross-sectional view showing an example of an apparatus inwhich vacuum plasma treatment is continually carried out. The treatmentsection which continually applies in vacuum plasma treatment to a longroll of film, which is continually conveyed, is constituted bypartitioned treatment chamber 12, having inlet 12A and outlet 12B forsample film F.

In the treatment chamber 12, facing electrodes 13 and 14 are provided.Of these paired electrodes 13 and 14, the electrode 13 is connected tohigh frequency power source 15, and the other electrode 15 is groundedemploying grounding cable 16. It is constituted so that an electricfield can be applied in the gap of paired electrodes 13 and 14.

Further, treatment gas is introduced from flow inlet 6 and air in thetreatment chamber is removed from flow outlet 7 employing an exhaustpump.

In the example in FIG. 2, pressure-reduced supplementary chambers 10 and11 are provided adjacent to the treatment chamber 12 on the film inletside. On the film outlet side, pressure-reduced supplementary chamber 17is provided. Further these are partitioned by nip rolls 8 and 9.Further, herein, 15 represents a high frequency power source.

When pressure-reduced supplementary chambers are provided, as shown inFIG. 2, 2 chambers on the film F inlet side and one chamber on theoutlet side may be provided. Embodiments may be considered in which onechamber is provided on the film F inlet side and one chamber on theoutlet side are provided, and two chambers on the film F inlet side andtwo chambers on the outlet side are provided.

Further, an apparatus which carries out flame plasma treatment, which isdescribed in Japanese Patent Publication Open to Public Inspection No.9-355097 is preferably employed.

Generally, a flame generated by a burner is composed of an inner flameand an exterior flame. The exterior flame is a part composed of the gasof the inner flame which is not combusted and heated, and commonly ispale blue. Thus the exterior flame is a so-called blue gas flame, andhas a relatively high temperature. The part of the flame, which is notblue, is the inner flame and has a relatively low temperature due to thelower supply of oxygen.

Said exterior flame is composed of a flame which is not required for theplasma treatment. When the exterior flame expands, it is impossible tocontrol the treatment. Therefore as shown in FIG. 3, shielding plate(exterior flame regulating shield) C is provided. By so doing,unnecessary exterior flame E′ is lead to the outside of the shield(exterior flame regulating shield) C and is remote from a support. Bybringing effective flame (regulated flame) G into contact with thesurface of sample film F, flame treatment is controlled, and theobjective is achieved. FIG. 3 shows burner B, exterior flame E, innerflame I, exterior flame E′ which is shielded by a shielding plate andlead to the outside of the shielding plate, effective flame G, effectivetreatment slit S, and the like, and a state in which effective flame Gis brought into contact with the surface of sample film F through theeffective treatment slit S.

The protective film of the present invention is subjected to plasmatreatment according to the method described above. Thereafter, it isadhered to a polarizer comprised of polyvinyl alcohol film, employing anadhesive to form a polarizing film. In the preferred method, a layercomprising hydrophilic high molecular compounds is further applied ontothe protective film. The resulting protective film is then adhered witha polarizer comprised of polyvinyl alcohol film to form a polarizingplate film. By employing high molecular compounds in the protectivefilm, which exhibit high affinity with a polarizer, it is possible tofurther improve the affinity and adhesive properties between thepolarizer and the protective film.

Plural times of plasma treatments are preferable.

The polarizing plate of the present invention will be described. Thepolarizing plate of the present invention is constituted in such amanner that a polarizer is sandwiched with a first protective film forthe polarizing plate and a second protective film for the polarizingplate. In at least one (preferably both) of the first protective filmfor the polarizing plate and the second protective film for thepolarizing plate, the protective film for the polarizing plate of thepresent invention is employed. By employing the protective film for thepolarizing plate of the present invention, it is possible to enhance thedurability, especially the durability at high humidity of the polarizingplate.

The liquid crystal apparatus of the present invention comprises a firstpolarizing plate, a liquid crystal cell, and a second polarizing plate,arranged in the interior of the first polarizing plate and the liquidcrystal cell. In addition to these, a light source as well as areflection plate may be provided. Herein, the first polarizing platecomprises a first protective film provided on the surface of the firstpolarizer on the side which faces neither the first polarizer nor theliquid crystal cell, and a second protective film provided on thesurface of the first polarizer on the side which faces the firstprotective film as well as the liquid crystal cell. Further, the secondpolarizing plate comprises a third protective film provided on thesurface of a polarizer on the side which faces the second polarizer aswell as the liquid crystal cell and a fourth protective film provided onthe surface of the second polarizer on the side which faces neither thethird protective film nor the liquid crystal cell. Further, theprotective film for the polarizing plate of the present invention isemployed as at least one (preferably all) of said first protective film,said second protective film, sand third protective film, and said fourthprotective film. By so doing, it is possible to enhance the durabilityof the polarizing plate, especially at high humidity.

Listed as hydrophilic polymers which are used for this purpose arehydrophilic cellulose derivatives (for instance, methyl cellulose,carboxymethyl cellulose, hydroxy cellulose, and the like), polyvinylalcohol derivatives (for example, polyvinyl alcohol, vinyl acetate-vinylalcohol copolymers, polyvinyl acetal, polyvinyl formal, polyvinylbenzyl, and the like), natural high molecular compounds (for example,gelatin, casein, gum arabic, and the like), hydrophilic polyesterderivatives (for example, partially sulfonated polyethyleneterephthalate, and the like), polyvinyl derivatives (for example,polyvinylpyrrolidone, polyacrylamide, polyvinyl imidazole, polyvinylpyrazole, and the like). Further, these hydrophilic polymers may beemployed individually or in combination.

In order to enhance adhesive properties of the aforementioned protectivefilm of the present invention with the polarizer, various compounds maybe incorporated into the aforementioned hydrophilic polymer layer or alayer comprising such compounds may be separately provided. Listed assuch compounds are those represented by general formula (1) or (2)described in Japanese Patent Publication Open to Public Inspection No.7-333436.

The present invention preferably comprises a layer containing compoundsrepresented by general formula (1) or (2).

A layer comprising such high molecular compounds having a carboxyl groupmay be employed along with the layer comprising the aforementionedhydrophilic high molecular compounds. However, it is preferably appliedto the protective film side of the layer comprising the aforementionedhydrophilic high molecular compounds. Namely, a layer comprisingcompounds represented by the general formula (1) or (2) is provided onthe protective film which has been subjected to plasma treatment.Thereafter, a layer comprising the aforementioned hydrophilic highmolecular compounds, which exhibits high affinity with a polarizer, ispreferably provided.

wherein A represent a structure unit formed through polymerization ofvinyl monomers, B represents a hydrogen atom, —CO—OM, or —CO—R, Mrepresents a hydrogen atom or a cation, and when Z=0, B represents ahydrogen atom. R represents —O—R′ or —N(R′)(R″), wherein R′ representsan alkyl group, an aralkyl group, an aryl group, a heterocyclic ringresidual group, or a non-metallic atom which is necessary to form aheterocyclic ring together with R″, R″ represents a hydrogen atom, alower alkyl group, or a non-metallic atom which is necessary to form aheterocyclic ring together with R′, R₁ and R₂ each represents a hydrogenatom, or a lower alkyl group, X represents —CO—O— or —O—CO—, R₃represents a halogenoalkyl group or a halogenoalkyloxyalkyl group, m, p,q, r, x, y, and z each represents a value of mole percent of eachmonomer, m and x each is 0 to 60, p, q, r, y, and z each is 0 to 100,m+p+q+r=100, x+y+z=100.

In the aforementioned general formulas (1) and (2), listed as vinylmonomers which form structural unit represented by A are, for example,styrene, styrene substituted with a nitro group, a fluorine atom, achlorine atom, a bromine atom, a chloromethyl group, a lower alkylgroup, and the like, vinyl methyl ether, vinyl ethyl ether, vinylchloroethyl ether, vinyl acetate, vinyl chloroacetate, vinyl propionate,unsaturated acids such as acrylic acid, methacrylic acid or itaconicacid, alkyl esters (said alkyl group is an unsubstituted alkyl grouphaving from 1 to 5 carbon atoms, or an alkyl group substituted with achlorine atom, a phenyl group, and the like) of acrylic acid ormethacrylic acid, phenyl esters (said phenyl group is an unsubstitutedphenyl group or a phenyl group substituted with a chlorine atom, aphenyl group, and the like) of acrylic acid or methacrylic acid,acrylonitrile, vinyl chloride, vinylidene chloride, ethylene,acrylamide, acrylamide substituted with an alkyl group having from 1 to5 carbon atoms, chlorine, a phenyl group, and the like, vinyl alcohol,glycidyl acrylate, acrolein, and the like. Of these, styrene, styrenehaving a substituent, vinyl acetate, vinyl methyl ether, alkyl acrylate,acrylonitrile, and the like are preferred.

Further, in the aforementioned formulas, the alkyl group represented byR′ has preferably from 1 to 24 carbon atoms and may be any of a straightchain alkyl group, a branched chain alkyl group, and a cycloalkyl group,and said alkyl group may have a substituent, which is a hydroxyl group,a hydroxycarbonyl group, —COOM′ group (wherein M represents a cation),and the like. Of these, specifically, a halogenoalkyl group substitutedwith a halogen atom such as fluorine, having from 2 to 18 carbon atomsor a halogenoalkyloxyalkyl group results in preferable results for thepurpose of the present invention. Preferred number of halogen atoms,which are substituted with said halogenoalkyl group and saidhalogenoalkyloxyalkyl group, is between 1 and 37. Said halogenoalkylgroup and halogenoalkyloxyalkyl group, and the halogenoalkyl group andhalogenoalkyloxyalkyl group represented by R₃ in the general formula (2)are preferably expressed by the following general formula (A):

wherein R₄, R₅, R₆, R₇, R₈, R₉, and R₁₀ each represents a hydrogen atomor a fluorine atom, n represents an integer of 1 to 12, n2 is 0 or 1,when n2 is 0, n1 is 0, when n2 is 1, n1 is 2 or 3, and n3 represents aninteger of 1 to 17. However, n1+n3 is 1 or 17. Further, when there areat least 2 R₄s in the general formula (A), they may be different such asthat one represents a hydrogen atom and the other represents a fluorineatom. In the same manner, when there are plurality of each of R₅, R₆,and R₇ in the general formula (A), they may represent different groups.

Further, in the aforementioned general formula (1), when R′ represents ahalogenoalkyl group or a halogenoalkyloxyalkyl group as described above,R in the aforementioned general formula (1) is preferably —O—R′.Further, there may be an aryl group such as phenol group or an aralkylgroup such as a benzyl group, represented by R′. Listed as thesesubstituents are a lower alkyl group substituted with a halogen atomsuch as a fluorine atom, a chlorine atom, bromine atom, and the like, ahydroxyl group, a hydroxycarbonyl group, a cationic oxycarbonyl group, anitrile group, a nitro group, and the like.

Further, heterocyclic rings represented by R′ or heterocyclic ringsformed by R′ and R″ are saturated or unsaturated heterocyclic ringscomprising a oxygen atom, a sulfur atom, or a nitrogen atom, andinclude, for example, heterocyclic rings selected from heterocyclicrings such as aziridine, pyrrole, pyrrolidine, pyrazole, imidazole,imidazoline, triazole, piperidine, piperazine, oxazine, morpholine,thiazine, and the like. Further, cations represented by M include thosesuch as a ammonium ion, a sodium ion, potassium ion, lithium ion, andthe like.

In the present invention, —COOM group containing high molecularcompounds, represented by the aforementioned general formula (1) or (2),are employed individually or in combination of two types or more, andthose having an average molecular weight of about 500 to about 500,000(weight average) are preferably employed.

Listed as the aforementioned representative high molecular compoundsemployed in the present invention can be those described below:

High molecular compounds having a —COOM group, represented by theaforementioned general formula (1) or (2) may be synthesized employingmethods known in the art. Namely, it is well known that maleic anhydridecopolymers are very common copolymers. Derivatives thereof are readilyobtained by allowing the maleic anhydride copolymer to react withalcohols or amines which match these. Further, alcohols or amines whichmatch maleic anhydride monomers are subjected to reaction and saidcompounds are obtained by copolymerizing the purified resultant productswith other vinyl monomers. Further, acrylates such as halogenoalkyl,halogenoalkyloxyalkyl, and the like are readily synthesized employingsynthetic methods of monomers and polymers described in Journal ofPolymer Science, 15 515 to 574 (1955) or British Patent No. 1,121,357.

The employed amount of high molecular compounds represented by thegeneral formula (1) or (2) is preferably between 10 and 1,000 mg/m², andis most preferably between 20 and 300 mg/m².

In the aforementioned embodiments of the present invention, theprotective film is provide with a layer (hereinafter occasionallyreferred to an upper layer) comprising at least one of theaforementioned hydrophilic high molecular compounds, and a layer(hereinafter occasionally referred to as a lower layer) comprising atleast one of high molecular compounds represented by the aforementionedgeneral formula (1) or (2), comprising at least one of theaforementioned hydrophilic high molecular compounds. For the protectivefilm, transparent resin films may be selected and employed. Suchtransparent plastic films include, for example, polyester films such aspolyethylene terephthalate film, polyethylene naphthalate, and the like,polyethylene film, polypropylene film, cellophane, diacetyl cellulosefilm, triacetyl cellulose film, cellulose acetate propionate, celluloseacetate butyrate film, polyvinyl chloride film, polyvinylidene chloridefilm, polyvinyl alcohol film, ethylenevinyl alcohol film, polystyrenefilm, syndioctatic polystyrene film, norbornane resin film,polycarbonate film, polyacrylate film, polymethyl methacrylate film,polyacrylate film, polyolefin based norbornane resin film,polymethylpentene film, polysulfone film, polyether ether ketone film,polyether sulfone film, polyether imide film, polyimide film, fluorineresin film, nylon film, acrylic film. In the present invention, otherthan cellulose triacetate film, due to excellent transparency, suitablyemployed are cellulose ester films such as cellulose diacetate,cellulose acetate butyrate, cellulose acetate phthalate, cellulosepropionate, and the like, polycarbonate film, polyester films such aspolyethylene terephthalate film, polyethylene naphthalate film, andpolyacryl films such as polymethyl methacrylate.

The thickness of the protective film is not particularly limited.However, from functions as well as ease of handling, the thickness ispreferably between 10 and 500 μm, and is most preferably between 30 and300 μm. if desired, UV absorbers, plasticizers, slipping agents, mattingagents and the like may be incorporated into the protective layer.

The aforementioned high molecular compounds and other additives, ifdesired, are dissolved in solvents or dispersed into the same, and acoating composition is prepared. The resulting coating composition isapplied onto the surface of the protective film, employing methods,known in the art, such as a gravure coater, a dip coater, a reverseroller coater, an extrusion coater, and the like. Thus theaforementioned layer is formed. The coated amount of the hydrophilichigh molecular compounds in the upper layer and of the aforementionedhigh molecular compounds in the lower layer is preferably between 10 and1,000 mg/m², and is more preferably between 20 and 300 mg/m² tospecifically obtain consistent adhesion force as well as excellentfinish quality after coating.

Drying methods after coating the aforementioned coating composition isnot particularly limited. However, it is preferable that the content ofthe residual solvent after drying is adjusted to no more than 5 percentby weight. The excessive content of the residual solvent is notpreferred because air bubbles are occasionally formed in the adhesioninterface between the polarizer and the laminated layer during dryingprocess.

If desired, UV absorbers, slipping agents, matting agents, antistaticagents, crosslinking agents, and surface active agents may beincorporated into the aforementioned layer coating composition of thepresent invention. The crosslinking agents are preferably incorporatedbecause they enhance adhesion with the polyvinyl alcohol film of thepolarizer. Listed as such crosslinking agents are, for example,polyvalent epoxy compounds, aziridine compounds, isocyanate compounds,alums, boron compounds, and the like.

Employed as adhesives, which are employed to adhere a polarizer with thesurface on an upper layer of the protective film having the upper andlower layers of the present invention, can be, for example, polyvinylalcohol based adhesives such as polyvinyl alcohol, polyvinyl butyral,and the like, vinyl based latexes such as butyl acrylate, and the like.

The polarizing plate of the present invention will be described. Thepolarizing plate of the present invention is constituted in such amanner that a polarizer is sandwiched with a first protective film forthe polarizing plate and a second protective film for the polarizingplate. In at least one (preferably both) of the first protective filmfor the polarizing plate and the second protective film for thepolarizing plate, the protective film for the polarizing plate of thepresent invention is employed. By employing the protective film for thepolarizing plate of the present invention, it is possible to enhance thedurability, especially the durability at high humidity of the polarizingplate.

The liquid crystal apparatus of the present invention comprises a firstpolarizing plate, a liquid crystal cell, and a second polarizing plate,arranged in the interior of the first polarizing plate and the liquidcrystal cell. In addition to these, a light source as well as areflection plate may be provided. Herein, the first polarizing platecomprises a first protective film provided on the surface of the firstpolarizer on the side which faces neither the first polarizer nor theliquid crystal cell, and a second protective film provided on thesurface of the first polarizer on the side which faces the firstprotective film as well as the liquid crystal cell. Further, the secondpolarizing plate comprises a third protective film provided on thesurface of a polarizer on the side which faces the second polarizer aswell as the liquid crystal cell and a fourth protective film provided onthe surface of the second polarizer on the side which faces neither thethird protective film nor the liquid crystal cell. Further, theprotective film for the polarizing plate of the present invention isemployed as at least one (preferably all) of said first protective film,said second protective film, sand third protective film, and said fourthprotective film. By so doing, it is possible to enhance the durabilityof the polarizing plate, especially at high humidity.

The embodiments of the present invention will be described.

A protective film for a polarizing plate characterized in that a contactangle with respect to pure water on the surface in contact with apolarizer is less than 55°.

The protective film for the polarizing plate described 1 above,characterized in that the surface in contact with a polarizer issubjected to hydrophilicity employing plasma treatment.

The protective film for the polarizing plate described in 1 or 2 above,characterized in that said plasma treatment is selected from vacuum glowdischarge, atmospheric pressure glow discharge and flame plasmatreatment.

A protective film for the polarizing plate characterized in comprising acoated layer containing at least one of hydrophilic high molecularcompounds on the surface which is subjected to plasma treatment.

The protective film of the polarizing plate described in 1, 2, 3 or 4above, characterized in that cellulose ester film, polycarbonate film,polyester film or polyacrylic film is employed.

A polarizing plate characterized in that the protective film for thepolarizing plate described in 1, 2, 3, 4, or 5 is employed.

In a production method of a polarizing plate in which a protective filmis adhered on at least one surface of a polarizer, a production methodof a polarizing plate characterized in that the surface a protectivefilm for the polarizing plate, which is adhered with a polarizer issubjected to plasma treatment prior to adhesion.

The production method of the polarizing plate described in 7,characterized in that the surface of the protective film for thepolarizing plate, which is adhered with a polarizer is subjected toplasma treatment, then to washing process, and is adhered with saidpolarizer.

In a production method in which at least one surface of a polarizer isadhered with a protective film for the polarizing plate, a productionmethod of a protective film for the polarizing plate characterized inthat the surface of said polarizer is subjected to plasma treatment, andthen adhered.

The production method of a polarizing plate described in 7 or 8,characterized in that the surface of a polarizer is subjected to plasmatreatment.

The production method of a polarizing plate described in any one ofclaims 7 through 10, characterized in that a protective film for thepolarizing plate in which before adhesion of a polarizer, the surface,which is adhered with said polarizer, is subjected to several plasmatreatments is employed.

The production method of a polarizing plate described in 11 above,characterized in that a protective film for the polarizing plate isemployed in which plasma treatment under conditions in which a C—C bondor a C—H bond of an organic substance on said film is broken, or anamino group is formed on the surface of said film is carried outsuccessively or simultaneously.

13. The production method of a polarizing plate described in 11 or 12above, characterized in that a protective film for the polarizing plateis employed, which is subjected to plasma treatment in the presence ofat least two gases selected from inert gases (argon, neon, and thelike), hydrogen, oxygen, hydrogen peroxide, ozone, carbon dioxide,carbon monoxide, nitrogen, nitrogen dioxide, nitrogen monoxide, watervapor, ammonia, and low boiling point organic compounds (lowerhydrocarbons, ketones, and the like).

14. The production method of a polarizing plate described in any one of11, 12, and 13, characterized in that a protective film for thepolarizing plate is employed, which is subjected to plasma treatment inthe presence of reaction gases comprising at least one of inert gases(argon, neon, and the like), hydrogen, water vapor, and hydrogenperoxide, and at least one of oxygen, water vapor, hydrogen peroxide,and ozone.

15. The production method of a polarizing plate described in any one of7 through 14 above, characterized in that a plasma treatment is selectedfrom a vacuum glow discharge, atmospheric pressure glow discharge, and aflame plasma treatment.

16. The protective film for the polarizing plate described in 1 through5 above, characterized in that an unevenness state of at least onesurface is in such that an average of central line average roughness Raof 10 points arbitrarily selected on said film is in the range of 1 to80 nm and an average of maximum height differences is in the range of 5to 80 nm.

17. The protective film for the polarizing plate described in any one of1 through 5 and 16 above, characterized in that the number of hydroxylgroups or amino groups which bond to a carbon atom on the surface ofsaid film is more than that of hydroxyl groups or amino groups whichbond to a carbon atom in the interior of the said film.

18. The protective film for the polarizing plate described in 1 through5, 16, and 17 above, characterized in that in the analysis of thebonding state of a carbon atom of said protective film for thepolarizing plate, employing X-ray photoelectron spectroscopy, when apeak having the lowest energy is designated as a first peak, the peakpositioned at 1.60±0.3 eV on the higher bonding energy side from thefirst peak is designated as a second peak, and the peak positioned at4.10±0.3 eV on the higher bonding energy side from the first peak isdesignated as a third peak, the bonding state of carbon atom C1s on thesurface of at least one surface and in the interior of said protectivefilm for the polarizing plate is in the relationship described below:S−I≧0.1

wherein S is the intensity of the second peak on the surface of saidprotective film for the polarizing plate/the intensity of the first peakon the surface of said protective film for the polarizing plate, and

I is the intensity of the second peak in the interior of said protectivefilm for the polarizing plate/the intensity of the first peak of theinterior of said protective film for the polarizing plate.

19. The protective film for the polarizing plate described in 1 through5, 16, and 17 above, characterized in that in the analysis of thebonding state of a carbon atom of said protective film for thepolarizing plate, employing X-ray photoelectron spectroscopy, when apeak having the lowest energy is designated as a first peak, the peaklocated at 1.60±0.3 eV on the higher bonding energy side from the firstpeak is designated as a second peak, and the peak positioned at 4.10±0.3eV on the higher bonding energy side from the first peak is designatedas a third peak, the bonding state of carbon atom C1s on at least onesurface of said protective film for the polarizing plate is in therelationship described below:S≧1.60

wherein S is the intensity of the second peak on the surface of saidprotective film for the polarizing plate/the intensity of the first peakon the surface of said protective film for the polarizing plate.

20. The protective film for the polarizing plate described in 1 through5, and 16 through 19 above, characterized in that in the analysis of thebonding state of a carbon atom of said protective film for thepolarizing plate, employing X-ray photoelectron spectroscopy, when apeak having the lowest energy is designated as a first peak, the peaklocated at 1.60±0.3 eV on the higher bonding energy side from the firstpeak is designated as a second peak, and the peak positioned at 4.10±0.3eV on the higher bonding energy side from the first peak is designatedas a third peak, the bonding state of carbon atom C1s on at least onesurface of said protective film for the polarizing plate is in therelationship described below:T≧0.2

wherein T is the intensity of the third peak on the surface of saidprotective film for the polarizing plate/the intensity of the secondpeak on the surface of said protective film for the polarizing plate.

21. A protective film for the polarizing plate characterized in thatplasma treatment under conditions in which a C—C bond or a C—H bond ofan organic substance on said film is broken, or an amino group is formedon the surface of said film is carried out successively orsimultaneously.

22. The protective film for the polarizing plate described in any one of1 through 5, and 16 through 21 above, characterized in that saidprotective film for the polarizing plate is subjected to plasmatreatment in the presence of at least two gases selected from inertgases, hydrogen, oxygen, hydrogen peroxide, ozone, carbon dioxide,carbon monoxide, nitrogen, nitrogen dioxide, nitrogen monoxide, watervapor, ammonia, and low boiling point organic compounds.

23. The protective film for the polarizing plate described in any one of1 through 5, and 16 through 22 above, characterized in that saidprotective film is subjected to plasma treatment in the presence ofreaction gases comprising at least one of inert gases, hydrogen, watervapor, and hydrogen peroxide, and at least one of oxygen, water vapor,hydrogen peroxide, and ozone.

24. The protective film for the polarizing plate described in any one of1 through 5, and 16 through 23 above, characterized in that the surfaceof said protective film for the polarizing plate is subjected to plasmatreatment, and thereafter is subjected water washing.

25. The protective film for the polarizing plate described in any one of16 through 25 above, characterized in comprising any of cellulose ester,polycarbonate, polyester and acrylic resins.

26. The polarizing plate characterized in that the protective film forthe polarizing plate described in 16 through 25 above is employed on atleast one surface.

27. A production method of a cellulose ester film characterized in thatcellulose ester separated from a polarizing plate employing celluloseester film which is subjected to plasma treatment is reused as all orsome of raw material.

28. A production method of a cellulose ester film characterized in thatthe protective film for the polarizing plate described in 1 through 5and 16 through 25 above comprises cellulose ester, and cellulose esterseparated from said protective film for the polarizing plate is reusedas all or some of the raw material for cellulose ester.

29. A production method of a cellulose ester film characterized in thatcellulose ester, which is separated from the polarizing plate filmdescribed in claim 26, is reused as all or some of the raw material forcellulose ester.

30. The production method of a cellulose ester film described in 29above, characterized in that a cellulose ester film is an optical filmemployed in an optical display apparatus.

The present invention will be described with reference to examplesbelow.

EXAMPLES Example 1

A plasma treatment was carried out as follows. Upper and lowerbrass-made electrodes having a diameter of 50 mm were provided in areaction vessel shown in FIG. 1, and a 100 μm thick polyimide asdielectric 3, which was larger than the electrode was adhered with theelectrodes. A 150×150 mm and 80 μm thick triacetyl cellulose film(Konica TAC KC8UVSF manufactured by Konica Corp., hereinafter referredto as TAC) was placed on the lower electrode. The gap between electrodeswas set at 20 mm, and air in the vessel was replaced with argon.

When the air is replaced with mixed gas, a high frequency voltage of3,000 Hz and 4,200 V was applied to said electrodes. A red-violet glowdischarge was then generated and a plasma was excited. Samples 1 and 2of the protective film for the polarizing plate were prepared throughtreatment of 5 and 20 seconds, respectively.

Example 2

Samples 3 and 4 of the protective film for the polarizing plate wereprepared in the same manner as Example 1, except that 10 percent ofargon gas was replaced with oxygen.

Example 3

Samples 5 and 6 of the protective film for the polarizing plate wereprepared in the same manner as Example 1, except that triacetylcellulose film (TAC film) employed in Examples 1 and 2 was replaced witha 75 μm thick polyethylene terephthalate film (PET film, trade nameDaiafoil, manufactured by Daiafoil Hoechst Co., Ltd.).

Example 4

Samples 7 and 8 of the protective film for the polarizing plate wereprepared in the same manner as Example 2, except that the TAC film wasreplaced with the PET film in Example 3.

Example 5

Samples 9 and 10 of the protective film for the polarizing plate wereprepared in the same manner as Example 1 and 2, except that the TAC filmwas replaced with a 75 μm thick polycarbonate film (PCfilm)(manufactured by Lonza Japan Co., Ltd.) and the 5-second treatmentwas only carried out.

Example 6

Samples 11 and 12 of the protective film for the polarizing plate wereprepared in the same manner as Example 5, except that the PC film wasreplaced with a 75 μm thick acrylate film (PMMA film) (manufactured byNihon Carbite Co., Ltd.) and the 20-second treatment was only carriedout.

Example 7

In the same manner as Examples 1 and 2, Samples 13 and 14 of theprotective film for the polarizing plate were prepared in such a mannerthat the coating composition having the composition described below wasapplied at 20 ml/m² onto the surface of a 80 μm thick TAC film, whichwas brought into contact with a polarizer, and subsequently dried at100° C. for 5 minutes.

(Coating Composition) <Lower Layer Coating Composition> Water-solublepolymer (mm) described below 0.5 g Acetone 40 ml Ethyl acetate 55 mlIsopropanol 5 ml <Upper Layer Coating Composition> Polyvinyl alcohol(Gosenol NH-26, 0.3 g manufactured by Nihon Gosei Kagaku Kogyo Co.,Ltd.) Saponin (surface active agent, manufactured 0.03 g by Merck Co.)Pure water 57 ml Methanol 40 ml Methylpropylene glycol 3 ml WaterSoluble polymer (m)

Comparative Example 1

The aforementioned TAC film, PET film, PC film, and PMMA film which werenot subjected to plasma treatment were designated as Samples 15, 16, 17,and 18, respectively.

Comparative Example 2

An 80 μm TAC film (Konica TAC KC8UVSF, manufactured by Konica Corp.) wasimmersed in a 2N sodium hydroxide solution at 60° C. for 30 seconds,washed with water, and subsequently dried. Thus a TAC film of whichsurface had been subjected to saponification was obtained. The resultingfilm was designated as Sample 19 of the protective film for thepolarizing plate.

Comparative Example 3

Sample 20 of the protective film for the polarizing plate was preparedin such a manner that one side of an 80 μm TAC film (Konica TAC KC8UVSF,manufactured by Konica Corp.) was subjected to corona dischargetreatment at conditions of 20 W/m²/minute. The corona dischargetreatment was carried out employing a corona treatment device having amulti-knife electrode of SOFTAL Co. The treatment conditions were asfollows: two treatments were carried out at a set energy of 40 W·min/m².

Table 1 shows conditions of the atmospheric pressure plasma treatment,which was applied to Samples 1 through 20 of the protective film, eachcontact angle, and evaluation results of adhesive properties when eachsample was employed to prepare a polarizing plate as described below.

A polarizing plate was prepared by adhering each of the aforementionedprotective film with a polarizer as described below.

An 18×5 cm size sample of the protective film was placed on a glassplate so that a surface which had been subjected to plasma treatment orcoating faces up.

A polarizer comprised of uniaxially stretched dyed polyvinyl alcoholfilm having the same size as the protective film sample was immersed in2 solid portion weight percent polyvinyl alcohol adhesive tank for 1 to2 seconds, and then adhered with both surface of the polarizer.

An Excessive adhesive, which was attached to the polarizer, was gentlywiped off, the resulting polarizer was placed the aforementionedprotective film sample, and was arranged in lamination so that thetreated surface of the sample film was brought into contact with theadhesive.

The excessive adhesive and air bubbles were removed from the edges ofthe aforementioned laminated polarizer and protective film employing ahand roller, and adhesion was carried out employing the same. Thepressure applied by said hand roller was set at about 0.2 to about 0.3Mpa and the speed was set at 2 m/minute. The sample obtained by 4. wasrested in a dryer at 80° C. for 2 minutes.

<Evaluation of Adhesive Properties>

(Initial Adhesion)

After adhering a polarizer with a protective film, peeling propertieswere manually evaluated. Evaluation was carried out at a 3 step grade, 1to 3, based on the degree of material destruction, as shown below.

1: major material destruction occurred. (in Table 1, shown by

2: partial material destruction occurred. However, the peeled area waslarge between the sample film and the PVA film. (in Table 1, shown by“B”)

3: peeling occurred between the sample film and the PVA film. (in Table1, shown by “C”)

(Machinability)

Cutting was carried out employing a single edge blade, and the degree ofseparation of the adhered surfaces was evaluated according to 3-grade, 1to 3, described below.

1: no separation of the adhered surfaces was observed. (in Table 1,shown by “A”)

2: slight separation of the adhered surfaces was observed. (in Table 1,shown by “B”)

3: major separation between adhered surfaces was observed. (in Table 1,shown by “C”)

(Durability)

Materials were stored at the condition (a) of 75° C. and 90% relativehumidity and the condition (b) of 90° C. for 500 hours, and any peeledwidth from the edge was measured. Symbols in Tables 1 indicates thefollowing.

A: within 0.5 mm

B: 0.6 to 1.5 mm

C: 1.6 mm or more

Further, adhesive properties, which are the same as Comparative Sample19 (the target of the present invention) or better than that, arecommercially viable. In Table 1, evaluation “A” is given. TABLE 1Condition Contact Adhesion property of Protective Transparent MainProcessing angle of polarising plate film resin component timeHydrophilic protective Initial No. film of gas (sec) layer film adhesionProcessability (a) (b) 1 TAC Ar 5 None 41 A A B A Inv. 2 TAC Ar 20 None39 A A A A Inv. 3 TAC Ar—O₂ 5 None 45 A A A A Inv. 4 TAC Ar 20 None 41 AA A A Inv. 5 PET Ar 5 None 46 A A B A Inv. 6 PET Ar 20 None 41 A A A AInv. 7 PET Ar—O₂ 5 None 47 A A B A Inv. 8 PET Ar—O₂ 20 None 42 A A A AInv. 9 PC Ar 5 None 42 A A B A Inv. 10 PC Ar—O₂ 5 None 41 A A A A Inv.11 PMMA Ar 20 None 43 A A B B Inv. 12 PMMA Ar—O₂ 20 None 40 A A A A Inv.13 TAC Ar 5 Provided 21 A A A A Inv. 14 TAC Ar—O₂ 5 Provided 18 A A A AInv. 15 TAC NP — None 60 C C C C Comp. 16 PET NP — None 71 C C C C Comp.17 PC NP — None 73 C C C C Comp. 18 PMMA NP — None 76 C C C C Comp. 19TAC Alkali — None 15 A A A A Comp. Saponification 20 TAC Corona — None55 C C C C Comp. DischargeNP: Not processed,Inv.: Invention,Comp.: Comparative

It is found that samples of the present invention exhibit excellentadhesive properties, as well as excellent machinability as a polarizingplate.

Example 8

Samples 21 and 22 of the protective film for the polarizing plate wereprepared in such a manner that an 80 μm thick TAC film (Konica TACKC8UVSF), manufactured by Konica Corp., was placed in a continuous typevacuum plasma discharge treatment apparatus, and was subjected to plasmatreatment in conditions of a power source frequency of 13.56 MHz, adischarge area of 0.08 m², a power source output of 8,000 W/m², a vacuumof 0.1 torr, and an introduced gas of either oxygen or nitrogen.

Example 9

Samples 23 and 24 were prepared in the same manner as Example 8, exceptthat the TAC film was replaced with at a 75 μm thick PET film.

Example 10

Samples 25 and 26 were prepared in such a manner that a coatingcomposition layer comprising hydrophilic compounds, which was preparedin the same manner as Example 7, was provided on the surface, which wasbrought into contact with a polarizer, of an 80 μm TAC film which hadbeen subjected to plasma treatment in the same manner as Example 8.

Table 2 shows vacuum plasma treatment conditions for Samples 21 through26 of the protective film, which have been subjected to plasmatreatment, measurement results of contact angles on the surface of saidprotective films, and evaluation results of adhesive properties whenpolarizing plates were prepared employing said protective films with theuse of the same method described above. TABLE 2 Condition ContactAdhesion property of Protective Transparent Processing angle ofpolarising plate film resin Reaction time Hydrophilic protective InitialNo. film gas (sec) layer film adhesion Processability (a) (b) 21 TACOxygen 10 None 38 A A A A Inv. 22 TAC Nitrogen 15 None 40 A A B A Inv.23 PET Oxygen 10 None 43 A A B A Inv. 24 PET Nitrogen 15 None 45 A A A AInv. 25 TAC Oxygen 10 Provided 21 A A A A Inv. 26 TAC Nitrogen 15Provided 20 A A A A Inv.Inv.: Invention

Example 11

An 80 m thick TAC film, manufactured by Konica Corp., was subjected toflame treatment in conditions shown in Table 3, employing a methoddescribed in Japanese Patent Publication Open to Public Inspection No.11-184042. FIG. 3 shows an employed apparatus. Further, contact time ofthe film with a flame was about 0.01 second. Samples 27 and 28 of theprotective film for the polarizing plate were prepared under conditionsin which said samples were subjected to effective plasma treatment. Suchconditions were as follows: the ratio a/b of the contact area a with aexterior flame to the maximum area of an inner flame b and the distancec (in mm) from the top of the inner flame were set as shown in Table 3.

The maximum area of the inner flame as described herein means a valueobtained by multiplying the central width of inner flame I in FIG. 3with the treated width of the film, and the contact area of the exteriorflame as described herein means a value obtained by multiplying thewidth of effective flame G (a part of the exterior flame) in contactwith a treated film with the treated width of the film.

Example 12

Samples 29 and 30 of the protective film for the polarizing plate wereprepared in the same manner as Example 11, except that the TAC film wasreplaced with a 75 μm thick PET film.

Example 13

Samples 31 and 32 were prepared in such a manner that a coated layercomprising hydrophilic compounds, which was prepared in the same manneras Example 7, was provided on the surface of a TAC film, which wasbrought into contact with a polarizer, which had been subjected toplasma treatment in the same manner as Example 11.

Example 14

A protective film for the polarizing plate was prepared in the samemanner as Sample 29 in Example 12 and further by providing a coatedlayer comprising hydrophilic compounds in the same manner as Example 7.The resulting sample was designated as Sample 33.

Table 3 shows flame plasma treatment conditions for Samples 27 through33 of the protective film, which have been subjected to plasmatreatment, measurement results of contact angles on the surface of saidprotective films, and evaluation results of adhesive properties whenpolarizing plates were prepared employing said protective films with theuse of the same method as described above. TABLE 3 Contact Adhesionproperty of Transparent Flame angle of polarising plate Protective resinCondition Hydrophilic protective Initial film No. film a/b c (mm) layerfilm adhesion Processability (a) (b) 27 TAC 1 5 None 38 A A A A Inv. 28TAC 5 5 None 40 A A B A Inv. 29 PET 5 5 None 43 A A B A Inv. 30 PET 5 10None 45 A A B B Inv. 31 TAC 1 5 Provided 20 A A A A Inv. 32 TAC 5 5Provided 20 A A A A Inv. 33 PET 5 5 Provided 19 A A A A Inv.

Example 15

An 80 μm thick-triacetyl cellulose film (Konica TAC KC8UX2MW,manufactured by Konica Corp.) was continually subjected to plasmatreatment at atmospheric pressure, employing an apparatus shown in FIG.2. Namely, air accompanied with a conveyed film was removed employing aroll. The resulting film was introduced into a chamber filled with areaction gas comprised of helium gas and water vapor, and was subjectedto plasma treatment at a power source frequency of 13.56 MHz and a powersource output of 8 kW/m². Thus a protective film was obtained.

A polyvinyl alcohol film (having a degree of polymerization of 4,000,manufactured by Kuraray Co., Ltd.) was uniaxially stretched (at astretching temperature of 110° C., and a stretching factor of 4.5) toobtain a polarizing base material. The resulting polarizing basematerial was immersed in an aqueous solution comprised ofiodine/potassium iodide/0.075 kg of water/5 kg/100 kg in ratio for 60seconds, while tension was applied, and subsequently was immersed in anaqueous boric acid containing solution comprised of potassiumiodide/boric acid/6 kg of water/7.5 kg/100 kg at 70° C. for 300 seconds.The resulting polarizing base material was washed with pure water, andsubsequently dried to prepare a polarizer. After drying, said polarizerwas adhered with a polyvinyl alcohol film which was supplied with apolyvinyl alcohol based adhesive on both sides at a pressure of 0.2 to0.3 Mpa and a speed of 2 m/min, employing the aforementioned roller, andwas stored at 80° C. for 2 minutes. The resulting material wasdesignated as Polarizing Plate A of the present invention.

Example 16

A polarizing plate was prepared in the same manner as Example 15, exceptthat after a triacetyl cellulose film was subjected to plasma treatment,the resulting film was washed with water at 40° C. and subsequentlydried. Said polarizing plate was designated as Polarizing Plate B of thepresent invention.

Example 17

A 40 μm thick triacetyl cellulose film (Konica TAC KC4UXMW, manufacturedby Konica Corp.) was continually subjected to plasma treatment atatmospheric pressure, employing an apparatus shown in FIG. 2. Namely,air accompanied with a conveyed film was removed employing a roll. Theresulting film was introduced into a chamber filled with a reaction gascomprised of argon gas containing 10 percent of oxygen and 4 percent ofhydrogen gas, and was subjected to plasma treatment at a power sourcefrequency of 13.56 MHz and a power source output of 8 kW/m².

A polyvinyl alcohol film (having a degree of polymerization of 4,000,manufactured by Kuraray Co., Ltd.) was uniaxially stretched (at astretching temperature of 110° C., and a stretching factor of 4.5) toobtain a polarizing base material. The resulting polarizing basematerial was immersed in an aqueous solution comprised ofiodine/potassium iodide/0.075 kg of water/5 kg/100 kg in ratio for 60seconds, while tension was applied, and subsequently was immersed in anaqueous boric acid containing solution comprised of potassiumiodide/boric acid/6 kg of water/7.5 kg/100 kg at 70° C. for 300 seconds.The resulting polarizing base material was washed with pure water, andsubsequently dried to prepare a polarizer. The resulting polyvinylalcohol film was continually subjected to plasma treatment atatmospheric pressure, employing an apparatus shown in FIG. 2. Namely,air accompanied with a conveyed film was removed employing a roll. Theresulting film was introduced into a chamber filled with a reaction gascomprised of argon gas and water vapor, and was subjected to plasmatreatment at a power source frequency of 13.56 MHz and a power sourceoutput of 8 kW/m². Said triacetyl cellulose film was adhered with apolyvinyl alcohol film which was supplied with a polyvinyl alcohol basedadhesive on both sides at a pressure of 0.2 to 0.3 Mpa and a speed of 2m/min, employing a roller, and was dried at 80° C. for 2 minutes. Theresulting material was designated as Polarizing Plate C of the presentinvention.

Example 18

An 80 μm thick triacetyl cellulose film (Konica TAC KC8UVSF,manufactured by Konica Corp.) was immersed in a sodium hydroxidesolution of 2 mole/liter at 60° C. for 90 seconds, washed with water andsubsequently dried. Thus said film was subjected saponification.

A polyvinyl-alcohol film (having a degree of polymerization of 4,000,manufactured by Kuraray Co., Ltd.) was uniaxially stretched (at astretching temperature of 110° C., and a stretching factor of 4.5) toobtain a polarizing base material. The resulting polarizing basematerial was immersed in an aqueous solution comprised ofiodine/potassium iodide/0.075 kg of water/5 kg/100 kg in ratio for 60seconds, while tension was applied, and subsequently was immersed in anaqueous boric acid containing solution comprised of potassiumiodide/boric acid/6 kg of water/7.5 kg/100 kg at 70° C. for 300 seconds.The resulting polarizing base material was washed with pure water, andsubsequently dried to prepare a polarizer. The resulting polyvinylalcohol film was continually subjected to plasma treatment atatmospheric pressure, employing an apparatus shown in FIG. 2. Namely,air accompanied with a conveyed film was removed employing a roll. Theresulting film was introduced into a chamber filled with a reaction gascomprised of argon gas and water vapor, and was subjected to plasmatreatment at a power source frequency of 13.56 MHz and a power sourceoutput of 8 kW/m². Said triacetyl cellulose film was adhered with apolyvinyl alcohol film which was supplied with a polyvinyl alcohol basedadhesive on both sides at a pressure of 0.2 to 0.3 Mpa and a speed of 2m/min, employing a roller, and was dried at 80° C. for 2 minutes. Theresulting material was designated as Polarizing Plate D of the presentinvention.

Example 19

An 80 μm thick cellulose acetate propionate film having the compositiondescribed below was subjected to plasma treatment in the same manner asExample 1, except that the mixed gas in the reaction vessel was replacedwith argon gas containing water vapor, having a relative humidity of 80percent. A polarizing plate was prepared in the same manner as Example17 employing the resulting cellulose triacetate propionate instead oftriacetyl cellulose film. The resulting material was designated asPolarizing Plate E of the present invention. <Cellulose AcetatePropionate Film> Cellulose acetate propionate (having a 100 kgsubstitution degree of the acetyl group of 2.0, and a substitutiondegree of the propionyl group of 0.8) Triphenyl phosphate 9 kgEthylphtharylethyl glycolate 4 kg Tinuvin 109 (manufactured by CibaSpecialty 1.1 kg Chemicals) Tinuvin 171 (manufactured by Ciba Specialty0.9 kg Chemicals) Aerojiru 200V (Nihon Aerijiru Co., Ltd.) 0.1 kg

Comparative Example 4

An 80 μm thick triacetyl cellulose film (Konica TAC KC8UX2MW,manufactured by Konica Corp.) was immersed in a solution of 2 moleKOH/liter at 60° C., washed with water, and subsequently dried to obtainTriacetyl Cellulose Film F.

A polyvinyl alcohol film (having a degree of polymerization of 4,000,manufactured by Kuraray Co., Ltd.) was uniaxially stretched (at astretching temperature of 110° C., and a stretching factor of 4.5) toobtain a polarizing base material. The resulting polarizing basematerial was immersed in an aqueous solution comprised ofiodine/potassium iodide/0.075 kg of water/5 kg/100 kg in ratio for 60seconds, while tension was applied, and subsequently was immersed in anaqueous boric acid containing solution comprised of potassiumiodide/boric acid/6 kg of water/7.5 kg/100 kg at 70° C. for 300 seconds.The resulting polarizing base material was washed with pure water, andsubsequently dried to prepare a polarizer. After drying, theaforementioned Triacetyl Cellulose Film F was adhered with a polyvinylalcohol film which was supplied with a polyvinyl alcohol based adhesiveon both sides at a pressure of 0.2 to 0.3 Mpa and a speed of 2 m/min,employing a hand roller, and was rested at 80° C. for 2 minutes. Theresulting material was designated as Comparative Polarizing Plate F ofthe present invention. In the same manner, Comparative Polarizing PlateG was prepared employing an 80 μm thick triacetyl cellulose film (KonicaTAC KC8UX2MW, manufactured by Konica Corp.) which was not subjected tothe aforementioned alkali treatment.

Machinability of Polarizing Plates A through E prepared in Examples 15through 19, as well as Comparative Polarizing Plates F and G prepared inComparative Example 4 were evaluated.

(Machinability)

Cutting was carried out employing a single edge blade, and the degree ofpeeling of adhered surfaces was evaluated according to 3 step grade, 1to 3, described below.

A: at the cut section of the polarizing plate, no peeling of the adheredsurfaces (between the cellulose ester film and the polyvinyl alcoholfilm) was observed.

B: at the cut section of the polarizing plate, peeling of the adheredsurfaces (between the cellulose ester film and the polyvinyl alcoholfilm) was partially observed.

C: at the cut section of the polarizing plate, major peeling of theadhered surfaces (between the cellulose ester film and the polyvinylalcohol film) was observed. TABLE 4 Polarizing Plate MachinabilityRemarks Polarizing Plate A A Present Invention Polarizing Plate B APresent Invention Polarizing Plate C A Present Invention PolarizingPlate D A Present Invention Polarizing Plate E A Present InventionPolarizing Plate F A Comparative Example Polarizing Plate G CComparative Example

As can be seen in Table 4, the polarizing plate of the present inventionexhibits excellent adhesion. Thus it has become possible to provide thesame machinability as the polarizing plate, in which a conventionalcellulose ester film which is subjected to saponification, is employed.

Example 20

An 80 μm thick triacetyl cellulose film (Konica TAC KV8UX2MW,manufactured by Konica Corp.) was subjected to plasma treatment in thesame manner as Example 1, except that the gas mixture in the reactionvessel was replaced with argon gas containing 4 percent of hydrogen.Further, said film was subjected to plasma treatment in the same mannerwhile the gas mixture in the reaction vessel was replaced with argon gascontaining water vapor with a relative humidity of 80 percent.

A polarizing plate was prepared in the same manner as Example 17,employing the resulting triacetyl cellulose, and was designated asPolarizing Plate H of the present invention.

The machinability was evaluated employing the same method as Example 19,and was graded to be A.

In order to evaluate the adhesion of adhered surfaces of PolarizingPlate H of the present invention H as well as Comparative PolarizingPlate F, the triacetyl cellulose film of the sectional part of the cutpolarizing plate was peeled off employing a cutter. When the triacetylcellulose film of both sides of peeled parts was pulled, the polyvinylalcohol film and the triacetyl cellulose film which compose bothpolarizers were hardly peeled off, and both triacetyl cellulose filmsthemselves were torn. As described above, it was confirmed thatPolarizer H of the present inventing has the same adhesion asComparative Polarizing Plate F.

Example 21

An 80 μm thick triacetyl cellulose film (Konica TAC KV8UX2MW,manufactured by Konica Corp.) was subjected to plasma treatment for 5seconds in the same manner as Example 1, except that the gas mixture inthe reaction vessel was replaced with argon gas containing 10 percent ofoxygen and 4 percent of hydrogen. The resulting triacetyl cellulose filmwas designated as Triacetyl Cellulose Film J.

A polarizing plate was prepared in the same manner as Example 17,employing said Triacetyl Cellulose Film J, and was designated asPolarizing Plate J of the present invention.

The adhesion of adhered surfaces of Polarizing Plate J was evaluatedemploying the same method as Example 20. As a result, it was confirmedthat Polarizing Plate J had the same adhesion as Polarizing Plate F.Comparative Polarizing Plate G prepared by employing a triacetylcellulose film which was not subjected to saponification was readilypeeled off and the adhesion was insufficient.

Measurement of surface roughness Ra as well as maximum height differenceP-V, and the analysis of carbon bonding state were carried out employingmethod described below for each of the aforementioned Polarizing PlateJ, Polarizing Plate F of Comparative Example 4, plasma-treated triacetylcellulose film and non-treated triacetyl cellulose employed in G, andsaponified triacetyl cellulose film (Triacetyl Cellulose Film F).

Measurement of Surface Roughness Ra and Maximum Height Difference P-V

A surface shape was measured under a dynamic mode (hereinafter referredto as DFM mode), employing a scanning type probe microscope SPI3800Nmultifunctional type unit SPA400 manufactured by Seiko Instruments. Theemployed cantilever was SI-DF20 (made of silicone, having a springconstant of 20.0 N/m, a torsion spring constant of 100.0 N/m, aresonance frequency of 120 to 150 Hz, a lever length of 200.0 μm, and aneedle height of 3.00 μm). A sample was cut into about 1 cm cube, whichwas placed on the leveled sample stand on a piezo scanner, and acantilever was allowed to approach the sample surface. When thecantilever reached a region in which an inter-atomic force works, scanwas carried out in the X and Y directions, and the unevenness of thesample was captured by piezo displacement in the Z direction. The piezoscanner was employed which was capable of scanning X, Y 20 μm, and Z 2μm. Scanning frequency was set at 1.00 Hz and a measurement area was setat 0.5×0.5 μm. The number of data for X and Y was 256 points,respectively. The obtained three-dimensional data were correctedemploying the first order gradient correction.

Analysis of Carbon Bond State

A QUANTUM-2000, manufactured by PHI Co. in the United Sates, wasemployed as a measurement instrument. Monochromatic Al X-ray source wasemployed and the beam diameter of X-ray was set at 100 μmφ. Spectra wereobtained by scanning said X-ray beam in an area of 1.5×0.1 mm. Regardingthe energy resolution, when Ag3d5/2 peak was measured employing acleaned Ag plate, its half bandwidth was 0.59 eV. Photoelectron emittingangle was 90°. For static charge correcting process, an electron beam aswell as an argon ion beam was employed (electrons were irradiated at 1eV, and ions were irradiated at 14 eV). Measured energy interval was setat interval of 0.05 eV, and integration was carried out until C1s peakreached 15,500 counts.

Surface and Interior

The measurement of the interior of a film can be carried out byemploying as a sample the surface obtained by shaving a film surfaceemploying a cleaned knife. In the present measurement, the followingmethod was employed. A film was adhered on a flat board (such as siliconwafer, slide glass, and the like) employing an adhesive so as to obtainflatness. The adhesive is selected which dissolves the film as little aspossible. In this measurement, an epoxy based adhesive was employed. Theedge of a glass knife in a microtome employed was arranged so as to bein parallel with the film surface and an about 0.8 μm surface layer wasshaved.

FIG. 4 shows surface photoelectron spectra. In FIG. 4, P₁, P₂, and P₃show a first peak, a second peak, and a third peak, respectively. S_(A)is the photoelectron spectrum of Cellulose Ester Film J (which wassubjected to plasma treatment), S_(B) is the spectrum of ComparativeCellulose Ester Film F (which was subjected to alkali saponification),and S_(C) is the spectrum of the untreated cellulose ester film.

Referring to photoelectron spectra which show the intensity of peaks onthe surface, as well as in the interior obtained as described above, theS, I, and T values, described below, which show the ratio of eachbonding state were obtained.

S=the intensity of the second peak on the surface of the protective filmfor the polarizing plate/the intensity of the first peak on the surfaceof the protective film for the polarizing plate

I=the intensity of the second peak on the interior of the protectivefilm for the polarizing plate/the intensity of the first peak on theinterior of the protective film for the polarizing plate

T=the intensity of the third peak on the surface of the protective filmfor the polarizing plate/the intensity of the second peak on the surfaceof the protective film for the polarizing plate

Table 5 shows measurement results of the surface roughness Ra as well asthe maximum height difference P-V, and analytical results of the carbonbonding state on the surface and the interior. TABLE 5 Ratio of SurfacePeak Intensity Roughness S I T Ra (nm) P − V (nm) Plasma 1.75 1.55 0.83.4 21 Treatment Saponification 4.42 4.41 0.1 0.6 3.0 Non-treatment 1.551.54 0.58 0.3 2.3

Example 22

Polarizers were separated and removed from cut scrap of the celluloseester film which was subjected to plasma treatment in Example 15 andPolarizing Plates A. Washed cellulose ester was dissolved in a mixedsolvent consisting of methylene chloride and ethanol (a mixed solvent of92 g of methylene chloride with 8 g of ethanol), and a dope having asolid portion concentration of 18 percent by weight was prepared. Theratio of the cellulose ester separated from the polarizing plates was 50percent of the total.

The resultant dope was filtered to remove foreign matter, and cast ontoa casting belt made of stainless steel maintained at 33° C. On saidcasting belt, the solvent was evaporated until the content of theresidual solvent became 80 percent. Thereafter, a resulting film waspeeled from the casting belt and subsequently dried at 100° C. Anobtained film was designated as Cellulose Ester film K of the presentinvention.

Polarizers were separated and removed from cut scrap of the celluloseester film which was subjected to alkali saponification in Example 4 andPolarizing Plates F. Washed cellulose ester was dissolved in a mixedsolvent consisting of methylene chloride and ethanol (a mixed solvent of92 g of methylene chloride with 8 g of ethanol), and a dope having asolid portion concentration of 18 percent by weight was prepared. Theratio of the cellulose ester separated from the polarizing plates was 50percent of the total. The resultant dope was filtered to remove foreignmatter, and in the same manner as above, cast onto a casting belt toprepare a cellulose ester film. An obtained film was designated asComparative Cellulose Ester film K of the present invention.

The 80 μm thick cellulose ester film prepared as described above wassandwiched with two polarizing plates. The polarizing plate was arrangedso that the stretching direction of the polarizer is in the right angle(cross Nicol state). Thereafter, one surface of the polarizing plate wasirradiated with light and the other surface was observed employing amicroscope (magnification factor of 30 under a transmission lightsource). The number of foreign particles, which looked white due tolight transmission, per 25 mm² was measured at four different areas. Theobtained number was denoted as one per 1 cm². The measurement wascarried out 5 times and the average was designated as the number ofluminescent spot foreign particles. Results showed that the number ofluminescent spot foreign particles of Cellulose Ester Film I of thepresent invention was 8/cm², while the number thereof of ComparativeCellulose Ester Film K was 62/cm². As shown in the results, CelluloseEster Film I of the present invention resulted in less number ofluminescent spot foreign particles. Thus it is found that the celluloseester film of the present invention is more suitable for recycling.

It has become possible to obtain a protective film for the polarizingplate employed as a liquid crystal element and the like withoutemploying chemicals for saponification, which are not preferred for workand complex processing, and thus to obtain a polarizing plate whichexhibits excellent machinability.

While the present invention has been described with reference tospecific embodiments thereof, it will be apparent to one skilled in theart that various changes and modifications can be made therein withoutdeparting from the spirit and scope thereof.

DESCRIPTION of REFERENCE NUMERALS AND SYMBOLS

-   1. electrodes-   2. F sample (film)-   3. dielectric-   4. and 6. flow inlet-   5. and 7. flow outlet-   8. and 9. nip roll-   10., 11., and 17. pressure-reduced supplementary chamber-   12. treatment chamber-   13. and 14. planar electrodes-   15. high frequency power source-   16. ground-   B burner-   C shielding plate-   E and E′ exterior flame-   I inner flame-   G effective flame-   R roller-   S effective treatment slit-   P₁, P₂, and P₃ photoelectron spectrum peak-   S_(A), S_(B), and S_(C) photoelectron spectrum

1: A producing method of an optical film, comprising: conducting a firstplasma treatment to a surface of a first resin film; obtaining a rawmaterial for making the optical film by utilizing at least a part of thefirst resin film; extruding the raw material to make a second resinfilm; and stretching the second resin film to make the optical film. 2:The producing method of claim 1, wherein the optical film is aprotective film for a polarizing plate. 3: The producing method of claim2, wherein the raw material are obtained by grinding at least the partof the first resin film and mixing the grinded at least the part of thefirst resin film with a cellulose ester powder. 4: The producing methodof claim 2, wherein the raw material does not include a cellulose esterfilm on which a saponification treatment is conducted. 5: The producingmethod of claim 1, wherein the first resin film is made of celluloseester. 6: The producing method of claim 1, wherein in analysis ofbonding state of a carbon atom employing X-ray photoelectronspectroscopy, when a peak having the lowest bonding energy is designatedas a first peak, a peak positioned at 1.60±0.3 eV on the higher bondingenergy side from the first peak is designated as a second peak, and apeak positioned at 4.10±0.3 eV on the higher bonding energy side fromthe first peak is designated as a third peak, bonding state of carbonatom C1s on a surface of at least one side of the first resin film andbonding state of internal carbon atom C1s in an optical depth of 0.05 to1 μm from the surface satisfy the following relationship:S−I≧0.1 where S is (intensity of the second peak on the first resin filmsurface/intensity of the first peak on the first resin film surface),and I is (intensity of the second peak in the interior of the firstresin film/intensity of the first peak of the interior of the firstresin film). 7: The producing method of claim 1, wherein the producingmethod further comprising: conducting a second plasma treatment to thestretched second resin film. 8: The producing method of claim 7, whereinin analysis of bonding state of a carbon atom employing X-rayphotoelectron spectroscopy, when a peak having the lowest bonding energyis designated as a first peak, a peak positioned at 1.60±0.3 eV on thehigher bonding energy side from the first peak is designated as a secondpeak, and a peak positioned at 4.10±0.3 eV on the higher bonding energyside from the first peak is designated as a third peak, bonding state ofcarbon atom C1s on a surface of at least one side of the optical filmand bonding state of internal carbon atom C1s in an optical depth of0.05 to 1 μm from the surface satisfy the following relationship:S−I≧0.1 where S is (intensity of the second peak on the optical filmsurface/intensity of the first peak on the optical film surface), and Iis (intensity of the second peak in the interior of the opticalfilm/intensity of the first peak of the interior of the optical film).9: The producing method of claim 8, wherein the following relationshipis satisfiedS−I≧0.15. 10: The producing method of claim 8, wherein S is 1.60 ormore. 11: The producing method of claim 8, wherein when a ratio ofrelative intensity of C1s peak is represented by T, which is (intensityof the third peak of the optical film surface/intensity of the secondpeak of the optical film surface), T is 0.2 or more. 12: The producingmethod of claim 1, wherein the first plasma treatment is an atmosphericpressure plasma treatment. 13: The producing method of claim 11, whereinthe atmospheric pressure plasma treatment is conducted in a gaseousmixture consisting of at least two types of gases selected from thegroup consisting of argon, neon, hydrogen, oxygen, hydrogen peroxide,ozone, carbon dioxide, carbon monoxide, nitrogen, nitrogen dioxide,nitrogen monoxide, water vapor, ammonia, ketone, and alcohol to make asurface of the resin film hydrophilic. 14: The producing method of claim6, wherein the second plasma treatment is an atmospheric pressure plasmatreatment. 15: The producing method of claim 14, wherein the atmosphericpressure plasma treatment is conducted in a gaseous mixture consistingof at least two types of gases selected from the group consisting ofargon, neon, hydrogen, oxygen, hydrogen peroxide, ozone, carbon dioxide,carbon monoxide, nitrogen, nitrogen dioxide, nitrogen monoxide, watervapor, ammonia, ketone, and alcohol to make a surface of the resin filmhydrophilic. 16: An optical film made by the producing method ofclaim
 1. 17: The optical film of claim 16, wherein the optical film is aprotective film for a polarizing plate. 18: An optical film made by theproducing method of claim 6, wherein in analysis of bonding state of acarbon atom employing X-ray photoelectron spectroscopy, when a peakhaving the lowest bonding energy is designated as a first peak, a peakpositioned at 1.60±0.3 eV on the higher bonding energy side from thefirst peak is designated as a second peak, and a peak positioned at4.10±0.3 eV on the higher bonding energy side from the first peak isdesignated as a third peak, bonding state of carbon atom C1s on asurface of at least one side of the optical film and bonding state ofinternal carbon atom C1s in an optical depth of 0.05 to 1 μm from thesurface satisfy the following relationship:S−I≧0.1 where S is (intensity of the second peak on the optical filmsurface/intensity of the first peak on the optical film surface), and Iis (intensity of the second peak in the interior of the opticalfilm/intensity of the first peak of the interior of the optical film).19: The optical film of claim 18, wherein S is 1.60 or more. 20: Theoptical film of claim 18, wherein when a ratio of relative intensity ofC1s peak is represented by T, which is (intensity of the third peak ofthe optical film surface/intensity of the second peak of the opticalfilm surface), T is 0.2 or more. 21: A polarizing plate comprising atleast the optical film of claim
 15. 22: A polarizing plate comprising atleast the optical film of claim 18.